## GeMS validation of OF-25-08_LaPlatasEMRI.gdb

File written by GeMS_ValidateDatabase.py, version of 02/19/2025
Tue Apr 28 11:34:28 2026
Runtime parameters
Database path: C:\Data\Pangaea\CGS\2025LaPlata\CO_2026_OF-25-08_LaPlataEMRI\OF-25-08_LaPlataEMRI_Publication\OF-25-08_LaPlataEMRI_Database\OF-25-08_LaPlatasEMRI.gdb
Output directory: C:\Data\Pangaea\CGS\2025LaPlata\CO_2026_OF-25-08_LaPlataEMRI\OF-25-08_LaPlataEMRI_Publication
Metadata file: C:\Data\Pangaea\CGS\2025LaPlata\CO_2026_OF-25-08_LaPlataEMRI\OF-25-08_LaPlataEMRI_Publication\OF-25-08_LaPlatasERMI-metadata.xml
Check embedded metadata: False
Skip topology check: False
Refresh GeoMaterialDict: True
Delete extra rows in Glossary and DataSources: False
Compact GDB: True
This database is LEVEL 3 COMPLIANT.
The database-level FGDC metadata are formally correct although the metadata record should be reviewed to verify that it is meaningful.
This file should be accompanied by OF-25-08_LaPlatasEMRI.gdb-ValidationErrors.html and OF-25-08_LaPlatasERMI-metadata.xml_errors.txt in the same directory.
If this database will be submitted to the NGMDB, it also needs to be accompanied by a reviewed Geologic Names report that includes identification of any suggested modifications to Geolex. Use the Geologic Names Check tool to generate that report or provide other documentation of a review.
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### Contents

Compliance Criteria
Warnings
Content not specified in GeMS schema
Occurrence of MapUnits in DMU, feature datasets, or geopackage tables
Contents of Nonspatial Tables
DataSources
DescriptionOfMapUnits
Glossary
MiscellaneousMapInformation
Database Inventory

### Compliance Criteria

#### LEVEL 1

Criteria for a LEVEL 1 GeMS database are:

- No overlaps or internal gaps in map-unit polygon layer
- Contacts and faults in single feature class
- Map-unit polygon boundaries are covered by contacts and faults lines

Databases with a variety of schema may meet these criteria. This script cannot confirm LEVEL 1 compliance.

#### LEVEL 2--MINIMALLY COMPLIANT

A LEVEL 2 GeMS database is accompanied by a peer-reviewed Geologic Names report, including identification of suggested modifications to Geolex, and meets the following criteria:

2.1 Has required elements: nonspatial tables DataSources, DescriptionOfMapUnits, GeoMaterialDict; feature dataset GeologicMap with feature classes ContactsAndFaults and MapUnitPolys | PASS
2.2 Required fields within required elements are present and correctly defined | PASS
2.3 All MapUnitPolys and ContactsAndFaults based feature classes obey Level 2 topology rules: no internal gaps or overlaps in MapUnitPolys, boundaries of MapUnitPolys are covered by ContactsAndFaults | PASS
2.4 All map units in MapUnitPolys have entries in DescriptionOfMapUnits table | PASS
2.5 No duplicate MapUnit values in DescriptionOfMapUnit table | PASS
2.6 Certain field values within required elements have entries in Glossary table | PASS
2.7 No duplicate Term values in Glossary table | PASS
2.8 All xxxSourceID values in required elements have entries in DataSources table | PASS
2.9 No duplicate DataSources_ID values in DataSources table | PASS

#### LEVEL 3--FULLY COMPLIANT

A LEVEL 3 GeMS database meets these additional criteria:

3.1 Table and field definitions beyond Level 2 conform to GeMS schema | PASS
3.2 All MapUnitPolys and ContactsAndFaults based feature classes obey Level 3 topology rules: No ContactsAndFaults overlaps, self-overlaps, or self-intersections. | PASS
3.3 No missing required values | PASS
3.4 No missing terms in Glossary | PASS
3.5 No unnecessary terms in Glossary | PASS
3.6 No missing sources in DataSources | PASS
3.7 No unnecessary sources in DataSources | PASS
3.8 No map units without entries in DescriptionOfMapUnits | PASS
3.9 No unnecessary map units in DescriptionOfMapUnits | PASS
3.10 HierarchyKey values in DescriptionOfMapUnits are unique and well formed | PASS
3.11 All values of GeoMaterial are defined in GeoMaterialDict. GeoMaterialDict is as specified in the GeMS standard | PASS
3.12 No duplicate _ID values | PASS
3.13 No zero-length, whitespace-only, or bad null values | PASS

### Warnings

There are 0 warnings

### Content not specified in GeMS schema

Some of the extensions to the GeMS schema identified here may be necessary to capture geologic content and are entirely appropriate. Please document these extensions in metadata for the database, any accompanying README file, and (if applicable) any transmittal letter that accompanies the dataset. Other extensions may be intermediate datasets, fields, or files that should be deleted before distribution of the database.

#### Fields

MapUnitLines, Type

#### Tables

FaultMovementAnno

### Occurrence of MapUnit in DMU, feature datasets, or geopackage tables

MapUnit | DescriptionOfMapUnits | GeologicMap
--- | --- | ---
Jjc | X | X
Qld | X | X
Qlsm | X | X
Qlsy | X | X
af | X | X
Ph | X | X
Qu | X | X
KPu | X | X
Qau | X | X
Qg | X | X
Qa | X | X
Qgl | X | X
Pc | X | X
Qtoo | X | X
Je | X | X
KPqm | X | X
Qac | X | X
Qto | X | X
Jm | X | X
KPgd | X | X
Ju | X | X
w | X | X
KPmp | X | X
mw | X | X
Kdb | X | X
KPsm | X | X
tails | X | X
TRd | X | X
Qay | X | X
Kch | X | X
KPm | X | X
KPg | X | X
Qaf | X | X
Qlso | X | X
Jw | X | X
Qti | X | X
Qc | X | X
Qrg | X | X
Qty | X | X
Kmf | X | X
Kpl | X | X
Qls | X | X
Qrgo | X | X
Qtu | X | X
snow | X | X
Qt | X | X
KPs | X | X
Qgo | X | X
Jjw | X | X
KPd | X | X
KPm/Pc | X | X
KPmd | X | X
Km | X | X

### Contents of Nonspatial Tables

#### DataSources

OBJECTID | Source | Notes | URL | DataSources_ID
--- | --- | --- | --- | ---
10 | Dictionary of geologic terms | American Geosciences Institute | https://information.americangeosciences.org/glossary | AGI
2 | Scott Lundstrum, this study | Geologic mapping | None | DAS1
3 | David Gonzales, this study | Igneous geologic mapping | None | DAS2
4 | Jacob Longridge, this study | Metallic minerals | None | DAS3
6 | Geology and ore deposits of the La Plata district, Colorado, E.B. Eckel | USGS Professional Paper 219 | https://doi.org/10.3133/pp219 | DAS5
7 | Geology and coal resources of the Durango area, La Plata and Montezuma Counties, Colorado, A.D. Zapp | USGS Oil and Gas Map OM-109 | https://ngmdb.usgs.gov/Prodesc/proddesc_5254.htm | DAS6
8 | Geology and fuel resources of the Red Mesa area, La Plata and Montezuma Counties, Colorado, Barnes, Harley, Baltz, E.H., Jr., and Hayes, P.T. | USGS Oil and Gas Map OM-149 | https://ngmdb.usgs.gov/Prodesc/proddesc_5297.htm | DAS7
11 | Dictionary | Meriam-Webster online dictionary | https://www.merriam-webster.com/ | DICT
1 | Federal Geographic Data Committee [prepared for the Federal Geographic Data Committee by the U.S. Geological Survey], 2006, FGDC Digital Cartographic Standard for Geologic Map Symbolization: Reston, Va., Federal Geographic Data Committee Document Number FGDC-STD-013-2006, 290 p., 2 plates. | None | https://ngmdb.usgs.gov/fgdc_gds/geolsymstd.php | FGDC-STD-013-2006
9 | GeMS standard | None | https://doi.org/10.3133/tm11B10 | GeMS
12 | USGS | Topographic base maps | https://apps.nationalmap.gov/downloader/ | USGS

#### DescriptionOfMapUnits

OBJECTID | MapUnit | Name | FullName | Age | Description | HierarchyKey | ParagraphStyle | Label | Symbol | AreaFillRGB | AreaFillPatternDescription | DescriptionSourceID | GeoMaterial | GeoMaterialConfidence | DescriptionOfMapUnits_ID
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
1851 | None | SURFICIAL DEPOSITS | None | None | In some cases, small outcrops of bedrock occur within areas of more extensive mapped Quaternary cover. | 01 | DMU-Heading1 | None | None | None | None | DAS1 | None | None | DMU1851
1908 | snow | Snow | Snow | Holocene | Late season snow patches in shaded high altitude basins above treeline based on available NAIP imagery. These few relatively small snow patches cover contacts, including morphology, tonal, vegetative and other field characteristics that would allow mapping of contacts and faults during most of the field season. | 01.01 | DMU Unit 1 (1st after heading) | snow | snow | None | 45° hatchure, 178-178-178, 0.7 pt, 4 pt. separation | DAS1 | Water or ice | High | DMU1908
1847 | None | HUMAN-MADE DEPOSITS | HUMAN-MADE DEPOSITS | None | None | 01.02 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1847
1848 | af | Artificial fill | Artificial fill | uppermost Holocene | Consists of fill and waste rock placed during construction of roads, mine facilities, and dams. Unit is composed mostly of unsorted silt, sand, and rock fragments but may include construction materials. Maximum thickness is up to 9 m (30 ft). Artificial fill may be subject to settlement when loaded, if not adequately compacted. | 01.02.01 | DMU Unit 1 | af | af | 255-255-255 | None | DAS1 | "Made" or human-engineered land | High | DMU1848
1849 | mw | Mine waste | Mine waste | uppermost Holocene | Includes rock debris in dump piles and in operational areas near mines. Maximum thickness is up to 12 m (40 ft). | 01.02.02 | DMU Unit 1 | mw | mw | None | 45° hatchure, 210-210-210 3 pt + 25-25-147 1 pt, 5 pt separation | DAS1 | "Made" or human-engineered land | High | DMU1849
1850 | tails | Tailings | Tailings | uppermost Holocene | Terraced tailings and waste rock of the Gold King Mill, La Plata valley near Boren Creek mouth. | 01.02.03 | DMU Unit 1 | tails | tails | None | 0° hatchure, 210-210-210 3 pt + 45° hatchure, 25-25-147 1 pt, 5 pt separation | DAS1 | Unmapped area | High | DMU1850
1912 | w | water | water | None | Water of lakes and reservoirs | 01.02.04 | DMU Unit 1 | w | w | 151-219-242 | None | DAS1 | Water or ice | High | DMU1912
1852 | None | ALLUVIAL DEPOSITS | ALLUVIAL DEPOSITS | None | Silt, sand, and gravel deposited in stream channels, flood plains, low terraces, and sheetwash areas along the La Plata and Mancos Rivers, Bear, Hermosa, Junction and Lightner creeks and their tributaries. Alluvial deposits locally include sheetwash, colluvium, or loess too small to be mapped at a scale of 1:24,000. | 01.03 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1852
1853 | Qa | Modern and recent alluvium including that of stream channels, valley floors, floodplains, and low terraces | Modern and recent alluvium including that of stream channels, valley floors, floodplains, and low terraces | Holocene | Includes alluvial deposits of the La Plata and Mancos Rivers, Bear, Cherry, Hermosa, Junction, and Lightner creeks and their tributaries, adjacent flood-plain deposits, and low-terrace alluvium that is up to 3 m (10 ft) above modern-stream level. Alluvium of these fluvial systems may include reworked glacial outwash. These deposits are mostly poorly sorted and clast supported. They consist of unconsolidated pebble, cobble, and locally boulder gravel in a sandy or silty matrix. Locally the unit is interbedded with or overlain by sandy silt and silty sand. Clasts are well rounded to subangular. Deposits contain clasts composed mostly of porphyritic rocks from the La Plata Mountains, various colored sandstone with lesser amounts of siltstone, conglomerate, and limestone; the clasts reflect the wide variety and distribution of intrusive and sedimentary rocks that crop out in each contributing watershed. Maximum thickness is estimated at 6 m (20 ft). Low-lying areas are subject to flooding. Unit may contain placer gold (Eckel, 1949) and is a source of sand and gravel. | 01.03.01 | DMU Unit 1 | Qa | Qa | 255-255-190 | None | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1853
1899 | Qay | Youngest alluvium of historically entrenched stream channels | Youngest alluvium of historically entrenched stream channels | upper Holocene | This unit is only mapped along lower Cherry Creek in the southern Thompson Park quadrangle where it forms alluvium of the entrenched modern alluvial channel, adjacent flood-plain deposits, and low-terrace alluvium that is up to 2 m (7 ft) above modern stream level. These deposits are mostly poorly sorted and clast- to matrix-supported. They consist of unconsolidated pebble, cobble, and locally boulder gravel in a sandy or silty matrix. Locally the unit is interbedded with or overlain by sandy silt and silty sand. Clasts are well rounded to subangular. Though uppermost Cherry Creek heads on the alpine landscapes of the south part of the La Plata Mountains, its alluvial character in a downstream direction is increasingly dominated by materials eroded from Cretaceous sedimentary rocks exposed within a semi-arid environment that produced entrenched arroyo and channel systems during the past two centuries in many parts of the Southwest (Bryan, 1925, Science, v. 62, p. 338-344) Thickness is estimated at 1-3 m (3-10 ft). Low-lying areas are subject to flooding. Unit may contain placer gold (Eckel, 1949) and is a source of sand and gravel. | 01.03.02 | DMU Unit 1 | Qay | Qay | 137-112-68 | None | DAS1 | None | None | DMU1899
1854 | Qac | Alluvium and colluvium, undivided | Alluvium and colluvium, undivided | Holocene and Upper Pleistocene | Unit chiefly consists of colluvium and sheetwash along valley sides. Locally includes debris-flow deposits and small subdued hills underlain by bedrock. The alluvial and colluvial deposits commonly are interfingered. Unit is poorly to well sorted and ranges from stratified pebbly sand and sandy gravel interbedded with sand (the alluvial component) to poorly sorted, poorly stratified clayey, silty sand, bouldery sand, and sandy silt (the colluvial component). Clast lithologies reflect that of the underlying bedrock and that subcropping and exposed directly upslope. Unit includes areas where deposits have ponded between lateral moraines of glacial unit Qg and adjoining slope above the local glacial limit. Thickness is commonly 1-3 m (3-10 ft); maximum thickness is estimated at about 10 m (30 ft). Low-lying areas are subject to flooding. Valley sides are prone to colluvial processes, sheetwash, rockfall, and small debris flows. Unit may be subject to settlement, collapse, or piping where fine grained and low in density. Unit is a potential source of sand and gravel. | 01.03.03 | DMU Unit 1 | Qac | Qac | 255-255-190 | ESRI 24k geology 602 255-0-0 | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1854
1855 | Qaf | Coarse alluvium and debris-flow deposits of alluvial fans | Coarse alluvium and debris-flow deposits of alluvial fans | Holocene and Upper Pleistocene | These deposits are mostly poorly sorted and clast supported. They consist of unconsolidated pebble, cobble, and locally boulder gravel in a sandy or silty matrix, and are distinguished from Unit Qa mainly by forming fan-shaped deposits at the mouths of tributary washes where they join higher-order alluvial drainages. Locally the unit is interbedded with or overlain by sandy silt and silty sand. Clasts are well rounded to subangular. Deposits contain clasts composed mostly of porphyritic rocks from the La Plata Mountains, various colored sandstone with lesser amounts of siltstone, conglomerate, and limestone; the clasts reflect the wide variety and distribution of intrusive and sedimentary rocks that crop out in each watershed. Locally includes debris-flow deposits or small subdued hills underlain by bedrock. Thickness is commonly 1-3 m (3-10 ft); maximum thickness is estimated at about 6 m (20 ft). Low-lying areas are subject to flooding. Valley sides are prone to colluvial processes, sheetwash, rockfall, and small debris flows. Unit may be subject to settlement, collapse, or piping where fine grained and low in density. Unit is a potential source of sand and gravel. | 01.03.04 | DMU Unit 1 | Qaf | Qaf | 255-255-115 | ESRI 24k geology 602 0-197-255 | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1855
1856 | Qau | Alluvial sediment including sheetwash | Alluvial sediment including sheetwash | Holocene to Upper Pleistocene? | Extensive areas of this unit cover the valley floors of Thompson Park south of Highway 160 and north of Menefee Mountain. This poorly exposed sheetwash alluvium overlies and is partly derived from broad areas of Mancos Shale (Km) as well as from flanking slopes that include reworked older Quaternary deposits, partly derived from sandstone of the Mesa Verde group formations. | 01.03.05 | DMU Unit 1 | Qau | Qau | 255-255-102 | ESRI 24k geology 602 137-68-68 | DAS1 | Alluvial sediment | High | DMU1856
1857 | None | COLLUVIAL DEPOSITS | None | None | Silt, sand, gravel, and clay on valley sides, valley floors, and hillslopes that were mobilized, transported, and deposited primarily by gravity. | 01.04 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1857
1858 | Qc | Colluvium | Colluvium | Holocene and Upper Pleistocene | Ranges from unsorted, clast-supported to matrix-supported, pebble to boulder gravel in a sandy or silty matrix to matrix-supported gravelly sand or clayey silt. Colluvium is derived from weathered bedrock and surficial deposits and is transported downslope primarily by gravity. Locally it grades to rock glacier deposits on flatter slopes and to debris-flow deposits in some drainages. Deposits are usually coarser grained in upper reaches and finer grained in distal areas. Deposits derived from thick, shale beds tend to be clay-rich and matrix supported. Colluvial deposits are unsorted or poorly sorted with weak or no stratification. Clast lithology is variable and depends on locally exposed material. The unit may include talus, landslide deposits, sheetwash deposits, and debris-flow deposits that are too small aerially or too indistinct on aerial photographs to be mapped separately. In a few areas within the La Plata Mountains, colluvium is present but not mapped to allow the bedrock relationships to be shown. Some deposits of colluvium likely include areas of shallow bedrock that are not depicted on the map. Exposures in these colluvial areas are very poor; hillslopes have a thin to moderate mantle of colluvial soils, and have thick vegetative cover, including extensive forests. Some areas mapped as colluvium grade into fan deposits (Qaf), and to unit Qac. Maximum thickness is estimated at 3-6 m (10-20 ft), but the unit commonly is much thinner. Areas mapped as colluvium are susceptible to future colluvial movement and deposition and locally subject to sheetwash, rockfall, small debris flows, mudflows, and landslides. Fine-grained, low-density colluvium may be prone to collapse upon wetting or loading. | 01.04.01 | DMU Unit 1 | Qc | Qc | 255-235-179 | None | DAS1 | Colluvium and other widespread mass-movement sediment | High | DMU1858
1859 | Qt | Talus | Talus | Holocene and Upper Pleistocene | Angular, cobbly, and bouldery rubble on moderate to steep slopes typically but not entirely below cliffs of intrusive lithologies and resistant sandstones within most Paleozoic and Mesozoic sedimentary bedrock units. Qt commonly lacks matrix at the surface. At depths greater than 70 cm (28 in), a poorly sorted loamy matrix (variable amounts of sand, silt and clay) is common, and Qt commonly is underlain by or incorporated into landslides. Unit forms steep slopes of largely treeless rubble adjoining areas of forested slopes, as well as adjoining areas of vegetated tundra meadows above the upper tree line. Past substantial downslope movement of meters to tens of meters makes the location of underlying bedrock contacts highly uncertain. Maximum thickness is estimated at 3 m (10 ft). Mapped areas are subject to severe avalanche, rockfall, rockslide, and rock-topple hazards. Talus may be a source of riprap. | 01.04.02 | DMU Unit 1 | Qt | Qt | 230-230-0 | random stipple 168-112-0 | DAS1 | Colluvium and other widespread mass-movement sediment | Medium | DMU1859
1861 | None | GLACIAL DEPOSITS | None | None | Gravel, sand, silt, and clay deposited by former glaciers of Pleistocene ice ages in most of the highest portions of major drainages of the map area, including the La Plata River and all three forks of the Mancos River, Bear Creek, South Fork of Hermosa Creek, and the highest tributary areas of Junction, Lightner, and Cherry creeks. Most glacial deposits as mapped in this area are likely to be largely to entirely late Pleistocene (Pinedale) age, due to the effects of obliterative overlap of successive glaciations, and to the active slope processes including erosion and mass movement on the steep slopes that dominate the La Plata mountains (accentuated by erosive effects of glaciation) which over lengthy time have removed deposits of earlier glaciations. Active slope processes on steep slopes also thwart recognition of the upper lateral limit of Late Pleistocene glacial deposits except where lateral moraine crests are preserved and mapped. | 01.05 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1861
1862 | Qg | Glacial till and associated deposits | Glacial till and associated deposits | Upper Pleistocene | This unit includes two types of deposits and landform suites that are gradational and not mapped separately. Glacial till of ground moraine of mid- to lower glaciated valley slopes that underly the bed of former glaciers ranges from thin (generally averaging less than 1 m in thickness) and discontinuous to locally up to 3 m thick in tributary valley bottoms, whereas till deposited in ice marginal positions as lateral and recessional moraines (in areas where associated moraine crests are mapped as line features) at the margins of the lower portions of paleoglaciers can be locally a few meters thick. Till of ground moraine and lateral moraines consists of poorly sorted diamicton that includes boulders, cobbles, and granule gravel, sand, silt and clay. Clasts range from subangular to subrounded including common faceted clasts that include glacial striations on favorable lithologies. The combined action of postglacial slope processes and soil development (largely associated with montane forest development and evolution) have imposed a colluvial forest soil complex on much of Qg in this area and most Qg is generally not exposed other than locally in roadcuts and landslide headscarps. Unmapped small bedrock outcrops occur within areas of ground moraine that forms the greater portion of mapped Qg including whalebacks and other glacially streamlined erosional forms but these small bedrock outcrops are greatly obscured by forest soil and colluvial cover. Qg may also include small areas of outwash and ice contact gravel deposited during deglaciation. Unit may contain placer gold (Eckel, 1949) and may be a source of sand and gravel. Thickness estimated at 1-4 m (3-13 ft). | 01.05.01 | DMU Unit 1 | Qg | Qg | 215-215-158 | ESRI 24k geology 502 255-170-0 | DAS1 | Glacial till | High | DMU1862
1863 | Qgl | Glacial deposits reworked by landslides | Glacial deposits reworked by landslides | Holocene and Upper Pleistocene | Glacial deposits reworked by landslides occur on the upper northern slope of Burro Mountain, where Late Pleistocene glacial till (Qg) overlies Mancos Shale (Km) and both units are likely involved in postglacial landslides. Surface material has the characteristics of unit Qg: Till of ground moraine and lateral moraines consists of poorly sorted diamicton that includes boulders, cobbles, granule gravel, sand, silt, and clay. Clasts range from subangular to subrounded including common faceted clasts that include glacial striations on favorable lithologies. The combined action of postglacial slope processes and soil development (largely associated with montane forest development and evolution) have imposed a colluvial forest soil complex on much of Qgl in this area and most Qgl is generally not exposed other than locally in roadcuts and landslide headscarps. Thickness estimated at 3-10 m (10-32 ft). | 01.05.02 | DMU Unit 1 | Qgl | Qgl | 215-215-158 | ESRI 24k geology 502 0-197-255 | DAS1 | Glacial till | High | DMU1863
1864 | Qgo | Older glacial till and associated deposits | Older glacial till and associated deposits | Middle (?) Pleistocene | This unit forms a few isolated remnants of end moraines that are down valley and beyond the limit of Qg. Partly correlative to Bull Lake age and marine isotope stage 6 (MIS 6). Till of end and lateral moraines consists of poorly sorted diamicton that includes boulders, cobbles, granule gravel, sand, silt, and clay. Clasts range from subangular to subrounded including common faceted clasts on favorable lithologies. The combined action of postglacial slope processes and soil development (largely associated with montane forest development and evolution) have imposed a colluvial forest soil complex on much of Qgo in this area and most Qgo is generally poorly exposed (other than locally in roadcuts and landslide headscarps). Unit may contain placer gold (Eckel, 1949) and may be a source of sand and gravel. Thickness from 2-6 m (6.5-20 ft). | 01.05.03 | DMU Unit 1 | Qgo | Qgo | 215-215-158 | ESRI 24k geology 502 169-0-230 | DAS1 | Glacial till | High | DMU1864
1865 | None | TERRACE ALLUVIUM | None | None | Terrace alluvium of the Mancos River system is chiefly glacial outwash. Terrace deposits locally include sheetwash, colluvium, or loess too small to be mapped at a scale of 1:24,000. The approximate terrace heights reported for each unit are the elevation differences measured between the adjacent modern stream valley and the top of the preserved deposit. The terraces converge in a downslope direction with the modern stream channels, so the corresponding heights of the terraces above local channels diminish in a downstream direction across the map area. | 01.06 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1865
1866 | Qty | Young terrace alluvium | Young terrace alluvium | Upper Pleistocene | Chiefly stream alluvium including glacial outwash that underlies terrace surfaces along or near the East Mancos River (below the confluence with the Middle Mancos River) and Cherry Creek and some of its tributaries including Starvation Creek. The unit is mostly poorly sorted, clast-supported, locally bouldery, pebble and cobble gravel in a silty or sandy matrix. It locally includes fine-grained overbank deposits or overlying sheetwash deposits. Clasts are mainly subround to round, and they are composed of the varied bedrock lithologies that crop out within the tributary drainage basins, including various porphyritic igneous rocks, sandstone of various colors, with lesser amounts of siltstone, conglomerate, and limestone. Clasts are generally unweathered or only slightly weathered. Thickness from 2-6 m (6.5-20 ft). | 01.06.01 | DMU Unit 1 | Qty | Qty | 255-255-190 | ESRI 24k geology 602 156-156-156 | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1866
1867 | Qti | Intermediate terrace alluvium | Intermediate terrace alluvium | Upper Pleistocene | Chiefly stream alluvium including glacial outwash that underlies several terrace surfaces along or near the East Mancos River. These terraces converge with modern channels in a downstream direction. Along the East Mancos River near the western mouth of its canyon through the Red Arrow-Caviness Dome, terraces associated with Qti are as much as 40 m (131 ft) above the river, whereas near the western edge of the quadrangle they are only 3-10 m (10-30 ft) above it. The western extent of Qti defines a paleovalley that crosses the modern East Mancos River and meets the West Mancos River system about one mile north of the present confluence of the East and West Mancos Rivers. The unit is mostly poorly sorted, clast-supported, locally bouldery, pebble and cobble gravel in a silty or sandy matrix. It includes fine-grained overbank deposits and overlying sheetwash deposits as well as variable eolian loess mantle that forms the upper part of the modern soil profile. Clasts are mainly subround to round, and they are composed of the varied bedrock lithologies that crop out within the drainage basin, including various porphyritic igneous rocks, sandstone of various colors, with lesser amounts of siltstone, conglomerate, and limestone. Clasts are generally unweathered or only slightly weathered. Sparse and poor exposures suggest Qti deposits are range from about 2-6 m (6.5-20 ft) thick. This unit is a source of sand and gravel and has been previously mined at several locations. It may contain placer gold (Eckel, 1949). | 01.06.02 | DMU Unit 1 | Qti | Qti | 255-255-190 | ESRI 24k geology 602 215-176-158 | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1867
1868 | Qto | Older terrace alluvium | Older terrace alluvium | Middle (?) Pleistocene | Chiefly stream alluvium including glacial outwash gravel and sand that underlies high terrace surfaces including that forming the present drainage divide between the East Mancos River and Cherry Creek. This high terrace surface represents a topographically inverted paleovalley formed along a former course of the East Mancos River that continued down East Canyon between Menefee Mountain on the west and the ridge crest that forms the county line south of Highway 160. Also included in Qto are high terrace surfaces flanking the West and Middle Mancos rivers at grades similarly about 100-130 m (300-400 ft) higher than the modern river valley floors. These terraces converge with modern channels in a downstream direction. Relative to the East Mancos River below the western mouth of its canyon through the Red Arrow-Caviness Dome, the Qto terrace is about 100 m (300 ft) higher, but the directional divergence in terrace and paleovalley from the East Mancos River course precludes grade and height comparison in a down valley direction. The unit is mostly poorly sorted, clast-supported, locally bouldery, pebble and cobble gravel in a silty or sandy matrix. It includes fine-grained overbank deposits and overlying sheetwash deposits as well as a variable eolian loess mantle that forms the upper part of the modern soil profile. Clasts are mainly subround to round, and they are composed of the varied bedrock lithologies that crop out within the East Mancos drainage basin, including various porphyritic igneous rocks, sandstone of various colors, with lesser amounts of siltstone, conglomerate, and limestone. Clasts are slightly to moderately weathered. Thickness from 2-6 m (6.5-20 ft). | 01.06.03 | DMU Unit 1 | Qto | Qto | 255-255-190 | ESRI 24k geology 602 255-170-0 | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1868
1869 | Qtoo | Ancient terrace alluvium | Ancient terrace alluvium | Middle (?) Pleistocene | Chiefly stream alluvium including glacial outwash gravel and sand that underlies relatively high terrace surfaces including part of the upland surface traversed by the Echo Basin Road west of the Middle Mancos River. This surface forms a less even and more undulating grade than that of younger terrace units, with the undulation attributed to mass movement and erosion of the flanking and underlying Mancos Shale (Km). Similarly high smaller terrace remnants of Qtoo include that of Airplane Ridge along the west edge of the map area and a higher terrace remnant flanking the west side of the main Qto surface forming the Mancos River-Cherry Creek divide north of Highway 160. The unit is mostly poorly sorted, clast-supported, locally bouldery, pebble and cobble gravel in a silty or sandy matrix. It includes fine-grained overbank deposits and overlying sheetwash deposits as well as an eolian loess mantle that forms the upper part of the modern soil profile. Clasts are mainly subround to round, and they are composed of the varied bedrock lithologies that crop out within the source drainage basins, including various porphyritic igneous rocks, sandstone of various colors, with lesser amounts of siltstone, conglomerate, and limestone. Clasts have different degrees of weathering. Thickness from 2-5 m (6.5-16 ft). | 01.06.04 | DMU Unit 1 | Qtoo | Qtoo | 255-255-102 | ESRI 24k geology 602 169-0-230 | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1869
1870 | Qtu | Undivided young and intermediate terrace alluvium | Undivided young and intermediate terrace alluvium | Upper Pleistocene | Chiefly stream alluvium that underlies several terrace surfaces along or near Cherry Creek. The unit is mostly poorly sorted, clast-supported, locally bouldery, pebble and cobble gravel in a silty or sandy matrix. It includes fine-grained overbank deposits and overlying sheetwash deposits as well as an eolian loess mantle that forms the upper part of the modern soil profile. Clasts are mainly subround to round, and they are composed of various porphyritic igneous rocks, sandstone of various colors, with lesser amounts of siltstone, conglomerate, and limestone. | 01.06.05 | DMU Unit 1 | Qtu | Qtu | 255-255-230 | ESRI 24k geology 602 255-224-0 | DAS1 | Alluvial sediment, mostly coarse-grained | High | DMU1870
1871 | None | LANDSLIDE DEPOSITS | None | None | A variety of types and relative ages of landslides are common and extensive in the mapped area, especially where underlying sedimentary bedrock units with steep to moderate slopes include shales and other mudstones. Landslide terrain is readily recognized in the field and in LiDAR imagery by hummocky topography, bounding headscarps, and lateral margins. Units of relatively younger and older age are only mapped where crosscutting relationships and morphology indicate contrasting ages of landslides are juxtaposed. | 01.07 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1871
1872 | Qls | Landslide deposits | Landslide deposits | Holocene and Pleistocene | Heterogeneous deposits consisting of unsorted, unstratified rock debris, sand, silt, clay, and gravel. Unit includes translational landslides, rotational landslides, earth flows, and extensive slope-failure complexes. Deposits range from active, slowly creeping landslides to long-inactive Pleistocene landslides. Many landslides involve the Mancos Shale, Dakota Sandstone/Burro Canyon Formation, Menefee Formation, Morrison Formation, Dolores Formation and various overlying surficial deposits. Maximum thickness may exceed 30 m (100 ft). Landslide deposits may be subject to future movement. Blocks of rock in these deposits may locally hinder excavation. Deposits may be prone to settlement when loaded. Shallow groundwater may occur within landslide deposits. | 01.07.01 | DMU Unit 1 | Qls | Qls | 255-235-102 | None | DAS1 | Mass movement sediment | High | DMU1872
1874 | Qlsy | Recent landslide deposits | Recent landslide deposits | upper Holocene | Includes several recently active landslides with fresh morphological features that suggest movement during the past several decades, such as along the north side of the West Mancos River canyon. Recent landslide deposits are heterogeneous and consist of unsorted, unstratified rock debris, clay, silt, and sand. Texture and clast lithology depend upon provenance area. Maximum thickness may exceed 10 m (30 ft). These deposits are prone to renewed or continued landsliding and may be susceptible to settlement when loaded. They also indicate the setting in which future slope failures will likely occur. Shallow groundwater may be present within areas mapped as recent landslide deposits. | 01.07.02 | DMU Unit 1 | Qlsy | Qlsy | 216-174-150 | None | DAS1 | Mass movement sediment | High | DMU1874
1873 | Qld | Landslide debris forming hummocky terrace over Mancos Shale | Landslide debris forming hummocky terrace over Mancos Shale | Pleistocene | Landslide debris forming hummocky terrace over Km (former valley floor) of Thompson Park and upper East Canyon. Debris is derived from erosional scarp retreat including various slope processes and mass-wasting of former Kpl cliff and scarp positions. Debris consists of blocks of sandstone ranging from pebbles to boulders more than 10 m (30 ft), derived from resistant beds of the Mesaverde Group especially that of the Point Lookout Sandstone, embedded in diamicton with sandy clay loam matrix partly derived from Mancos Shale. Thickness from 2-20(?) m (6.5-65 ft). | 01.07.03 | DMU Unit 1 | Qld | Qld | 216-174-0 | None | DAS1 | Mass movement sediment | High | DMU1873
1876 | Qlso | Older landslide deposits | Older landslide deposits | Pleistocene | Heterogeneous deposits consisting of unsorted, unstratified rock debris, sand, silt, clay, and gravel. This unit is mapped based on hummocky but relatively old landslide terrain in juxtaposition with Qls that has relatively fresh morphology. Qlso may nonetheless include older translational landslides, rotational landslides, earth flows, and extensive slope-failure complexes that have potential to become reactivated. Maximum thickness may exceed 30 m (100 ft). Landslide deposits may be subject to future movement. Deposits may be prone to settlement when loaded. Shallow groundwater may occur within landslide deposits. | 01.07.04 | DMU Unit 1 | Qlso | Qlso | 168-112-0 | None | DAS1 | Mass movement sediment | High | DMU1876
1875 | Qlsm | Landslide complex of various age and activity on slopes overlying and derived from Mancos Shale (Km) | Landslide complex of various age and activity on slopes overlying and derived from Mancos Shale (Km) | Pleistocene | Heterogeneous deposits consisting of unsorted, unstratified rock debris, sand, silt, clay, and gravel. This unit is mapped for hummocky forested slopes underlain by Mancos Shale (Km) that indicate the inclusion of relatively old landslides that do not have the relatively fresh morphology of Qls. Qlsm may include older translational landslides, rotational landslides, earth flows, and extensive slope-failure complexes that have potential to become reactivated. Maximum thickness may exceed 30 m (100 ft). Landslide deposits may be subject to future movement. Blocks of rock in these deposits may locally hinder excavation. Deposits may be prone to settlement when loaded. Shallow groundwater may occur within landslide deposits. | 01.07.05 | DMU Unit 1 | Qlsm | Qlsm | 200-178-102 | None | DAS1 | Mass movement sediment | High | DMU1875
1877 | None | ROCK GLACIERS | None | None | None | 01.08 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1877
1878 | Qrg | Rock glaciers and associated deposits | Rock glaciers and associated deposits | Holocene and Upper Pleistocene | Coarse, angular boulder gravel similar to and gradational to talus (Qt) that show distinctive surface morphology as evidence of rock glacier flow, including single and multiple transverse and longitudinal ridges that are subparallel to steep rock glacier margins, some near angle of repose. The upper part of many rock glaciers is gradational to steep talus slopes which can be mapped separately in some locations where an intervening depression occurs; this may be seasonally occupied by remnant snow. These features are recognized on the basis of morphology in many high alpine settings of Colorado. A few rare exposures support the hypothesis that downslope flow is related to existence of partial ice cores and ice matrix during the recent millennia; in some cases an ice core may remain. The remnant ice core, which can be considered a type of permafrost, is thermally insulated by the overlying rocky debris cover. The boulder rubble appears clast supported and openwork on the surface but the space between clasts is filled with a sandy diamict at depth, usually within 1 m (3 ft) of the surface. Qrg occurs in the highest cliff-flanked alpine environments including cirques, generally above the upper treeline but also sharply flanking and forming enclaves within higher parts of forested areas. Where underlying bedrock, especially the Mancos Shale, is conducive to mass movement, and occurs in sufficiently rugged and cold alpine environments such as in the alpine setting of the northwestern La Plata Mountains, Qrg is more extensive and may be partly gradational to even more extensive landslide deposits (Qls). A range of formation age and activity is included in this unit. In cirques at the head of glaciated valleys, Qrg is post-glacial (Holocene), but Qrg in areas that lack clear glacial evidence could include Late Pleistocene remnants. Rock glacier morphology ranges from having very steep fronts that suggest ongoing flow activity to more subdued morphology in which previous ice cores have dissipated, giving the rock glacier a deflated appearance. Rock glaciers in the Rocky Mountain region include those of the Little Ice Age (~A.D. 1300 to 1850) (rock glaciers with relatively active morphology and weathering characteristics), earlier neoglacial and possibly early Holocene age. Thickness ranges from 2-20 m (6.5-65 ft). | 01.08.01 | DMU Unit 1 | Qrg | Qrg | 255-255-190 | ESRI 24k geology 605 255-158-15 | DAS1 | Glacial till | Medium | DMU1878
1879 | Qrgo | Older rock glacier remnants and associated deposits | Older rock glacier remnants and associated deposits | Holocene and Upper Pleistocene | Locally subdivided from unit Qrg, (see description of Qrg) where they distinctively adjoin younger Qrg but do not contain active morphology. Qrgo also forms isolated remnants, including that covered by forest in downvalley locations. Thickness from 2-20 m (6.5-65 ft). | 01.08.02 | DMU Unit 1 | Qrgo | Qrgo | 255-255-190 | ESRI 24k geology 605 171-205-102 | DAS1 | Glacial till | Medium | DMU1879
1881 | Qu | Undivided Quaternary deposits | Undivided Quaternary deposits | Holocene and Pleistocene | This unit is mapped where an unclear composite of more than one of the units described above comprise a partly colluvial diamict cover that buries bedrock contacts. Unit may locally include glacial and landslide deposits. | 01.08.03 | DMU Unit 1 | Qu | Qu | 255-255-230 | None | DAS1 | Sediment | High | DMU1881
1882 | None | BEDROCK GEOLOGY | None | None | None | 02 | DMU-Heading1 | None | None | None | None | DAS1 | None | None | DMU1882
1898 | None | HYPABYSSAL IGNEOUS ROCKS | None | None | Mapping and description of intrusive rocks in the La Plata quadrangle are largely from David Gonzales and Jacob Longridge and are significantly revised from Eckel (1949). Outside of the area of central stock, monzonite porphyry is dominant within the mapped area forming sills, dikes, and irregular masses There is a continuum of compositional variation between gabbro, diorite, monzodiorite, monzonite, granodiorite, and syenite. This relationship is well illustrated by the intrusive rocks exposed in Columbus Basin where monzonite porphyry grades into lesser zones of diorite and monzodiorite. Age constraints of intrusive rocks in the La Plata Mountains range from 75-67 Ma (Gonzales, 2025, and ages reported in this study). | 02.01 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1898
1914 | KPsm | Syenite and monzonite | Syenite and monzonite | Paleocene (?) to Upper Cretaceous | This is a dominant rock type exposed in the Allard stock and outlying exposures in Boren Creek. The rocks vary from medium- to coarse-grained equigranular to porphyritic phaneritic. The textural variations are interpreted as different cooling rates within the plutons. The dominant constituents in this rock unit are perthitic orthoclase with lesser sodic plagioclase (AN 35 or less); in some thin sections, quartz was noted but its origin is uncertain. Mafic minerals are subordinate and make up less than 10% of samples. All feldspar has minor to extensive degrees of alteration to sericite and clay minerals. Biotite was noted in several samples and has minor to extensive alteration to chlorite and opaque minerals. Outlines of crystals that appear to have been hornblende were also observed in some thin sections, but these are completely pseudomorphed by chlorite and opaque minerals. Euhedral to subhedral apatite in single crystals or clusters are common in these rocks. There is no petrographic evidence to support the idea that there are mafic syenites and felsic syenites as proposed by Werle et al. (1984), and syenite appears to be compositional gradational with monzonite in the Allard stock. Most of the samples have stockwork breccia filled with veinlets of quartz + chalcedony + calcite ± chlorite + Fe oxide + pyrite ± chalcopyrite ± sphalerite ± fluorite. Rutile was noted in quartz in some thin sections. Perthitic orthoclase from a pegmatitic zone within the Allard stock yielded an Ar-Ar plateau age of 68.32 ± 0.04 Ma (personal communication with Matt Heizler, April 2021). | 02.01.01 | DMU Unit 1 | KPsm | KPsm | 213-75-0 | None | None | None | None | DMU1914
1900 | KPs | Syenite porphyry | Syenite porphyry | Paleocene (?) to Upper Cretaceous | Light-brown to medium-gray syenite porphyry is exposed on the west side of the quadrangle at Jackson Ridge. The rock weathers reddish brown to light tan. These rocks have a pronounced hiatal porphyritic texture defined by laths and blades of orthoclase and plagioclase up to 1 cm in length. The phenocrysts are set in a very fine-grained matrix composed mostly of feldspar. The color index of these rocks is less than 5%. Feldspar and groundmass phenocrysts are extensively altered to secondary sericite and mafic minerals and opaques are replaced by iron oxide. Masses of secondary calcite are also noted in these rocks. An Ar-Ar plateau age of 70.81 ± 0.11 Ma for feldspar was determined for a sample collected on Jackson Ridge. The age spectrum is disturbed, and the assigned age represents a maximum. Total fusion, normal isochron and reverse isochron analyses yielded ages of 71.99 ± 0.13 Ma, 70.85 ± 0.57 Ma, and 70.85 ± 0.57 Ma, respectively. The analyses indicated a low temperature 40Ar (rad) argon loss pattern with an erratic K/Ca spectrum indicative of the sample alteration (reported by Daniel Miggins, Oregon State University, January 8, 2026). | 02.01.02 | DMU Unit 1 | KPs | KPs | 255-102-0 | None | DAS2 | Fine-grained, felsic-composition intrusive igneous rock | High | DMU1900
1901 | KPqm | Quartz monzonite or syenite | Quartz monzonite or syenite | Paleocene (?) to Upper Cretaceous | Brownish orange to medium brown on weathered and fresh surfaces. Exposures are found near the headwaters of Boren Creek. Rock is coarse grained and equigranular. The dominant constituents are quartz and feldspar, and the color index is less than 10%. This is one of the few intrusive rocks that contain abundant and visible quartz in hand specimen. The rock is altered and has iron oxide coatings and fillings over the entire outcrop. | 02.01.03 | DMU Unit 1 | KPqm | KPqm | 178-178-235 | None | DAS2 | Coarse-grained, felsic-composition intrusive igneous rock | Medium | DMU1901
1902 | KPgd | Granodiorite | Granodiorite | Paleocene (?) to Upper Cretaceous | Light to medium gray on weathered surface to dark gray on fresh surfaces. Mostly medium- to coarse-grained and typically equigranular except along margins where it is finer grained. In some outcrops, the feldspar phenocrysts are distinctly larger than the groundmass. This rock type is exposed in Basin Creek to the east and was mapped by Eckel (1949) as diorite. In several locations the stock is cut by quartz monzonite dikes, sills, and small offshoots. Near the Tomahawk mill in Basin Creek, granodiorite is injected and brecciated by stringers of quartz monzonite. The dominant constituents in the granodiorite are perthitic orthoclase and plagioclase (oligoclase to andesine) and green hornblende. Quartz makes up less than a few percent of the essential minerals and is late in the crystallization history, confined to the groundmass. Accessory minerals include apatite, opaque minerals, sphene, and zircon. There is incipient alteration of feldspar to sericite and other clay minerals, and minor recrystallization to epidote. Hornblende is altered to varying degrees to chlorite and opaque minerals. There are also masses of epidote + chlorite + calcite + muscovite in this groundmass defining a deuteric propylitic alteration assemblage. | 02.01.04 | DMU Unit 1 | KPgd | KPgd | 204-153-204 | None | DAS2 | Coarse-grained, intermediate-composition intrusive igneous rock | High | DMU1902
1903 | KPm | Augite monzonite-central stock | Augite monzonite-central stock | Paleocene (?) to Upper Cretaceous | Light gray to medium gray on weathered surfaces. This rock makes up the central stock exposed at Babcock Peak, Mount Moss, and Lavender Peak. This rock is mostly medium- to coarse-grained and equigranular with <10% phenocrysts. The dominant constituents are subhedral to euhedral perthitic orthoclase and plagioclase (oligoclase to low andesine) up to 8 mm in maximum dimension. Quartz makes up less than a few percent of the rocks and is a late-stage phase that crystallized mostly between feldspar. Augite and green hornblende ± biotite are the dominant varietal minerals along with accessory apatite, opaque minerals, sphene ± zircon. Augite is mantled by hornblende indicating an increase in hydrous conditions during crystallization. Hornblende is commonly altered to chlorite + iron oxide and feldspar is altered to variable degrees to sericite and clay minerals. Epidote is found in the groundmass as a replacement mineral in feldspar in some samples, and masses of calcite are also noted in the groundmass. A sample collected near the north flank of Lavender Peak yielded a U-Pb zircon age of 67.150 ± 0.033 Ma. This was confirmed by an Ar-Ar plateau age of 67.37 ± 0.16 Ma for pyroxene for a sample collected on the south flank of Babcock Peak (reported by Daniel Miggins, Oregon State University, January 8, 2026). The similarity of the two ages within analytical uncertainty indicates that the stock underwent rapid cooling upon emplacement. | 02.01.05 | DMU Unit 1 | KPm | KPm | 255-170-0 | None | DAS1 | Coarse-grained, intermediate-composition intrusive igneous rock | High | DMU1903
1917 | KPm/Pc | Monzonite porphyry sill complex and Cutler Formation, undivided | Monzonite porphyry sill complex and Cutler Formation, undivided | Paleocene (?) to Upper Cretaceous and Lower Permian | Poorly exposed area of KPmp sills and dikes intruding Late Paleozoic Cutler Formation (Pc). Though Eckel (1949) schematically mapped numerous sills within the area of this map unit, the dominantly steep, forested and colluviated slopes lack outcrops except where exposed along roads that obliquely cross bedding and sills. The lack of geomorphic expression and forest cover prohibit mapping of sill distribution in this area. | 02.01.06 | DMU Unit 1 | KPm/Pc | KPm/Pc | 255-170-0 | 45° hatchure, 0-197-255, 4 pt separation | DAS1 | Coarse-grained, intermediate-composition intrusive igneous rock | Medium | DMU1917
1904 | KPmp | Monzonite porphyry | Monzonite porphyry | Paleocene (?) to Upper Cretaceous | Light-tan to light-gray monzonite porphyry that weathers reddish brown to brown. This is the dominant intrusive rock type within the quadrangle forming large sill-shaped plutons, sills, dikes, and irregular masses. There is a continuum of compositional variation between diorite, monzodiorite, quartz monzonite-monzonite, and granodiorite. This relationship is well illustrated by the intrusive rocks exposed in Columbus Basin where outcrops of monzonite porphyry grade into smaller zones of diorite and monzodiorite. The monzonite porphyry contains 20 to 40% phenocrysts and microphenocrysts (0.5 to 1 cm in size) of euhedral to subhedral tabular orthoclase and plagioclase (albite to oligoclase) set in a medium- to coarse-grained groundmass dominated by feathery masses of altered feldspar. Proportions of plagioclase and orthoclase are variable, but in most samples there is a higher percentage of plagioclase. All the feldspar has pronounced zonation indicative of rapid cooling and disequilibrium crystallization. Late-stage quartz crystallized in the groundmass between the feldspar. Euhedral to subhedral hornblende is the only mafic phase observed, commonly as phenocrysts. Near the eastern extent of Columbus Basin phenocrysts of hornblende up to 5 cm long were noted. In some samples there is a secondary blue-green amphibole that forms needles that replaced early hornblende and is also noted within alteration assemblages in the groundmass. Accessory minerals include apatite, sphene, and opaque minerals. Feldspar commonly has a pronounced oscillatory zoning indicative of rapid cooling and disequilibrium crystallization. Masses of epidote were noted in plagioclase and hornblende and calcite ± epidote ± chlorite were observed in the groundmass assemblages and some hornblende crystals. Typically, plagioclase is often partially recrystallized to masses of epidote, sericite, and calcite. Orthoclase phenocrysts typically show complete or near complete alteration to sericite and clay minerals, and hornblende is altered to varying degrees to chlorite + iron oxide. Most opaque minerals are also oxidized to different degrees to limonite and hematite. The dominant alteration assemblages are indicative of late-stage volatile enrichment and deuteric recrystallization. Xenoliths up to 10+ cm in dimension are common in the monzonite porphyry and include felsic to mafic gneiss and schist, granite, and various sedimentary lithologies. An Ar-Ar plateau age of 68.14 ± 0.08 Ma was determined for feldspar from a sample collected on in Columbus Basin (reported by Daniel Miggins, Oregon State University, January 8, 2026). The analysis yielded a very discordant age spectrum due to alteration of feldspar. Gonzales (2015) reported an Ar-Ar age for samples of monzonite of 70.36 ± 0.86 Ma and 75.19 ± 0.66 Ma suggesting that the monzonite plutons were emplaced over a period of millions of years. | 02.01.07 | DMU Unit 1 | KPmp | KPmp | 255-0-0 | None | DAS1 | Fine-grained, intermediate-composition intrusive igneous rock | High | DMU1904
1905 | KPmd | Monzodiorite porphyry | Monzodiorite Porphyry | Paleocene (?) to Upper Cretaceous | Medium brown to orangish brown on weathered surfaces and light brown on fresh surfaces. A prominent exposure of monzodiorite porphyry is the intrusive mass exposed at the base of Hesperus Mountain and forms the prominent ridge west of the peak. Smaller exposures are found within monzonite porphyry. The monzodiorite contains phenocrysts of blocky oligoclase and orthoclase up to 6 mm in maximum dimension set in a finer-grained groundmass dominated by feldspar. Euhedral to subhedral phenocrysts of hornblende up to 3 mm in maximum dimension make up 20% to 30% of the rock. Accessory minerals include apatite, opaque minerals, and titanite (sphene). There is incipient to moderate alteration of feldspar to sericite ± kaolinite + other clay minerals, and hornblende is generally altered to calcite + chlorite. Masses of calcite often occur in the groundmass assemblages. | 02.01.08 | DMU Unit 1 | KPmd | KPmd | 225-150-200 | None | DAS1 | Fine-grained, intermediate-composition intrusive igneous rock | High | DMU1905
1906 | KPd | Diorite porphyry | Diorite porphyry | Paleocene (?) to Upper Cretaceous | Light- to medium-gray on weathered surface and darker gray on fresh surfaces. This rock forms dikes and sills of variable dimensions. Some sills are tens of meters thick and extend over hundreds of meters. These rocks are distinguished by 20 to 50% phenocrysts of hornblende up to 2 cm in length. The rock also contains subhedral to euhedral crystals of plagioclase ranging from 1 mm to 5 mm long. The phenocrysts are set in a medium- to coarse-grained groundmass of hornblende, plagioclase, opaque minerals, and apatite ± sphene. Plagioclase crystals occur as laths to tabular, sub-equant crystals, typically have a pronounced oscillatory zoning, and locally define a weak flow lineation. The groundmass in most samples is a feathery to granular mass of recrystallized and altered feldspar. Deuteric recrystallization and alteration are developed to varying degrees in all samples. Hornblende is typically altered to chlorite while feldspar phenocrysts are recrystallized to aggregates of sericite, clay, calcite, and epidote. Groundmass plagioclase is generally more altered than the phenocrysts. One of the distinct features of diorite plutons is the presence of cogenetic hornblende-rich inclusions and xenoliths of felsic to mafic schist and gneiss, granite, sandstone, shale, siltstone, and rare limestone. The hornblendite inclusions are interpreted as accumulations of fractionated hornblende during magma crystallization. Inclusions and xenoliths range from 1 cm to tens of cm in maximum dimension. In some outcrops the xenoliths make up to 40% of the rock. Outcrops of diorite porphyry are typically cut by numerous joints that are interpreted as cooling features. Gonzales (2015) reports an Ar-Ar age for hornblende for two diorite samples of 68.25 ± 0.44 Ma and 68.41 ± 0.92, respectively. A dark grayish-green to black diorite porphyry dike cuts the Cutler Formation north of Falls Creek in "Dike Creek" canyon in the eastern part of the Monument Hill quadrangle. The dike is porphyritic to microporphyritic and is composed of less than 10% phenocrysts of andesine and augite that are less than 2 mm in length. The groundmass is a very fine-grained assemblage composed essentially of andesine and augite with lesser amounts of apatite, opaque minerals, biotite, and quartz. Alteration of the groundmass is extensive and consists of epidote, calcite, sericite, and chlorite. In outcrop this dike reaches a maximum thickness of about 4.6 m (15 ft) and has a pronounced columnar jointing developed at right angles to its margins. | 02.01.09 | DMU Unit 1 | KPd | KPd | 245-136-237 | None | DAS2 | Coarse-grained, intermediate-composition intrusive igneous rock | High | DMU1906
1913 | KPg | Gabbro (lamprophyre) | Gabbro (lamprophyre) | Paleocene (?) to Upper Cretaceous | Dark green to greenish black porphyritic rock with phenocrysts of augite and hornblende up to 1 cm long set in a fine-grained groundmass composed chiefly of hornblende and plagioclase with opaque minerals, apatite ± sphene. Phenocrysts comprise up to 40% of the rock. Most of the gabbro plutons are dikes and sills up to several m thick, but an extensive exposure crops out at the base of the sill on Indian Trail Ridge. On Indian Trail Ridge, the gabbro and diorite are gradational possibly related by fractionation of hornblende and pyroxene (Rogers and Longshore, 1960). Alteration in these rocks is incipient to moderate with chlorite replacement of mafic phenocrysts, clay alteration of plagioclase, and blebs of calcite ± chlorite ± epidote within the groundmass. Eckel (1949) mapped the gabbro as lamprophyre. An Ar-Ar plateau age of 68.68 ± 0.08 Ma was determined for hornblende from a sample of gabbro collected on Indian Ridge (reported by Daniel Miggins, Oregon State University, January 8, 2026). This age is consistent with an Ar-Ar age of 67.02 ± 0.41 Ma reported by Gonzales (2015) for a sample of gabbro. | 02.01.10 | DMU Unit 1 | KPg | KPg | 168-0-0 | None | DAS2 | Coarse-grained, mafic-composition intrusive igneous rock | Medium | DMU1913
1907 | KPu | Undivided intrusive igneous rocks | Undivided intrusive igneous rocks | Paleocene (?) to Upper Cretaceous | Most of this unit comprises igneous sills and connecting dikes in the Monument Hill quadrangle. Many are dominated by monzonite porphyry (Kmp), to which the description for that unit applies herein. | 02.01.11 | DMU Unit 1 | KPu | KPu | 252-223-248 | None | DAS1 | Intrusive igneous rock | High | DMU1907
1883 | None | SEDIMENTARY BEDROCK UNITS | None | None | None | 02.02 | DMU-Heading2 | None | None | None | None | DAS1 | None | None | DMU1883
1916 | None | Mesaverde Group | Mesaverde Group | Upper Cretaceous | Consists of three mapped formations in the Thompson Park quadrangle, which, in descending order, are the Cliff House Sandstone, Menefee Formation, and Point Lookout Sandstone. These formations are distinguished primarily by the carbonaceous shale and coal within the Menefee Formation and the presence of Ophiomorpha burrows in the Cliff House Sandstone and Point Lookout Sandstone. The Point Lookout Sandstone and resistant sandstone beds in the Menefee Formation locally form prominent cliffs in the quadrangle. | 02.02.01 | DMU-Heading3 | None | None | None | None | None | None | None | DMU1916
1884 | Kch | Cliff House Sandstone | Cliff House Sandstone | Upper Cretaceous | Interbedded sequence of moderately hard, yellowish-orange to white, very fine- to fine-grained calcareous sandstone and light-gray mudstone, siltstone, and silty shale. Sandstone beds contain locally abundant Ophiomorpha burrows. The sandstone beds weather to yellowish brown or light reddish brown, forming a rusty-colored outcrop that forms cliffs and ledges and that sharply contrasts with the drab colors of the underlying Menefee Formation. The Cliff House Sandstone forms many of the broad, rounded ridges in the southwestern part of the mapped area. Individual sandstone beds within the Cliff House Formation thicken west of the mapped area. Barnes and others (1954) described sandstone beds up to 4 m (14 ft) thick on Weber Mountain south of the town of Mancos. In Mesa Verde National Park, sandstone beds are as much as 15-20 m thick. To the east, shale and siltstone beds thicken and sandstone beds thin. Contact with the underlying Menefee Formation appears to be conformable and gradational in most of the quadrangle. Barnes and others (1954) described local intertonguing of the Cliff House Sandstone and Menefee Formation. The Cliff House Sandstone is a transgressive, shallow marine unit deposited on the upper shoreface zone of a barrier-island beach front (Siemers and King, 1974). The overlying Lewis Shale has been eroded from the mapped area, and the stratigraphically highest exposed beds of Cliff House Sandstone form a resistant, erosional upper surface to mesas and buttes at the south end of the mapped area, thus the maximum thickness about 120 m (400 ft) in the mapped area is less than the original thickness. Shale beds in the Cliff House Sandstone may have moderate to high swell potential. The formation is an important natural gas reservoir and producer in the San Juan Basin. | 02.02.01.01 | DMU Unit 1 | Kch | Kch | 176-204-137 | 135° hatchure, 197-0-255, 1 pt line, 5 pt separation | DAS1 | Mostly sandstone | High | DMU1884
1887 | Kmf | Menefee Formation | Menefee Formation | Upper Cretaceous | Interbedded gray, brown, and black carbonaceous shale and siltstone, light-gray, brown, and orange-brown, locally lenticular, crossbedded sandstone, and coal. Locally includes burnt rock and clinker resulting from burning of coal beds within the formation. Sandstone beds are commonly well cemented and locally form prominent ledges. They also contain ripple marks and sometimes have abundant organic debris. Contact with the underlying Point Lookout Sandstone is conformable, but commonly sharp. It is placed at the base of the lowest coal or carbonaceous shale bed. The Menefee Formation was deposited in a coastal-plain environment (Aubrey, 1991). Thickness is variable, ranging from about 100-130 m (330-430 ft). The variation is partly due to syn-depositional factors, such as the possible intertonguing between the Menefee Formation and Cliff House Sandstone, but also to differential compaction of the sand, clay, and especially the peat beds during lithification. Thickness variations are also related to volume loss due to combustion of coal beds. Subsidence of the land surface may occur above underground mines where coal was extracted from the Menefee Formation. Burning coal beds and seepage of methane or hydrogen sulfide from coal outcrops can be hazardous. Sandstone beds in the formation may cause local rockfall hazards. | 02.02.01.02 | DMU Unit 1 | Kmf | Kmf | 176-204-137 | 0° hatchure, 255-255-0, 0.5 pt dotted line, 5 pt separation | DAS1 | Sandstone and mudstone | Medium | DMU1887
1888 | Kpl | Point Lookout Sandstone | Point Lookout Sandstone | Upper Cretaceous | This formation includes an upper part dominated by relatively massive sandstone beds and a lower part with a greater amount of shale interbedded with sandstone. The upper part (30 m thick) consists of thick, massive beds of light-gray to yellowish-gray or brown, quartzose sandstone, with minor interbeds of dark-gray shale. The sandstone is fine- to medium-grained, cross-laminated, well sorted, and cemented with calcite. Locally, the massive part contains Ophiomorpha burrows. The massive part of the Point Lookout Sandstone may pose rockfall hazards where exposed in steep cliffs. The lower part consists of interbedded thin sandstone and shale beds between the massive part of the Point Lookout Sandstone and the Mancos Shale. In the lower part, sandstone beds are less than one meter thick and consist of light-gray to yellowish-gray or brown quartzose sandstone. Shale beds are light to dark gray, fossiliferous, and carbonaceous, and become more abundant towards the base of the unit. The lower part of the Point Lookout Sandstone is usually poorly exposed. West of the quadrangle, near the town of Mancos, Barnes and others (1954) and Condon (1990) described intertonguing relationships between the massive and lower parts, including an area where massive sandstone beds occur at both the top and base of the formation. The formation consists of sandstone lenses that are stacked in an imbricate pattern and separated by shale and siltstone of varying thickness. The younger beds lie to the northeast. The formation was deposited in a coastal shoreline environment as a deltaic plain and mouthbar depositional sequence (Wright, 1986, Wright-Dunbar and others, 1992). The Point Lookout Sandstone represents an eastward prograding shoreline between the sea in which the Mancos Shale was deposited and the coastal plain where the Menefee Formation was accumulating. Contact with underlying Mancos Shale is conformable. Thickness averages 80 m (250 ft). Shale beds in the lower part may have high swell potential. It is prone to landsliding, and soil slips are common in residuum and colluvium derived from the unit. The Point Lookout Sandstone is an important reservoir and producer of natural gas in the San Juan Basin. | 02.02.01.03 | DMU Unit 1 | Kpl | Kpl | 163-255-115 | None | DAS1 | Mostly sandstone | High | DMU1888
1886 | Km | Mancos Shale | Manocs Shale | Upper Cretaceous | Dark-gray to black shale and silty shale, dark-gray to blue-gray argillaceous limestone, and calcarenite with thin beds of bentonite. Unmapped landslide deposits locally overlie the Mancos Shale. Yellowish-brown to dark-brown weathered concretions form within the calcareous basal part of the formation. The Mancos Shale is generally very poorly exposed within the mapped area. West of the mapped area in and near Mesa Verde National Park, Leckie and others (1997) subdivided it into eight members. In ascending order, these members are the Graneros, Bridge Creek, Fairport, Blue Hill, Juana Lopez, Montezuma Valley, Smoky Hill, and Cortez members. Leckie and others (1997) described 188 bentonite beds, most of which are less than 10 cm (4 in) thick, within the Mancos Shale. They occur throughout the formation but are most abundant in the lower one-fourth of the unit. The contact with the underlying Dakota Sandstone is conformable. The Mancos Shale was deposited in a low-energy, marine environment. Total thickness of the Mancos Shale is about 650-760 m (2,000-2,500 ft). Our mapping of this unit may include the lowermost shale-rich part of the Point Lookout Formation due to poor exposures and a gradational contact. The Mancos Shale is prone to landsliding. Bentonitic beds may cause expansive soil and heaving bedrock problems. Unit is rich in sulfate, which can be corrosive to concrete and may affect the quality of groundwater. | 02.02.02 | DMU Unit 1 | Km | Km | 176-204-137 | None | DAS1 | Mostly mudstone | High | DMU1886
1885 | Kdb | Dakota Sandstone and Burro Canyon Formation, undivided | Dakota Sandstone and Burro Canyon Formation, undivided | Upper Cretaceous and Lower Cretaceous | Dakota Sandstone is composed of light- to medium-gray, light- to medium-brown, and yellowish-brown, fine- to coarse-grained sandstone and minor conglomeratic sandstone and conglomerate that is interbedded with dark- to medium-gray siltstone, carbonaceous shale, and thin coal beds. Conglomerate clasts in the Dakota Sandstone usually are granules and pebbles of chert and quartz. The underlying Burro Canyon Formation consists of very light-brown to very light-gray, medium- to coarse-grained sandstone, chert-pebble conglomerate, and grayish-green, non-carbonaceous claystone. The absence of coal and carbonaceous shale and the presence of green claystone and white (kaolinitic?) clasts and cement in the Burro Canyon Formation are the primary characteristics used to distinguish it from the Dakota Sandstone (Turmelle, 1979). The white clasts are rich in clay and mica and contain relict features suggestive of altered phenocrysts. The Dakota Sandstone and Burro Canyon Formation are lumped into a single map unit because surficial deposits usually either conceal the contact between the two formations, or it occurs in a near vertical cliff or very steep hillslope and is not possible to depict on a map at a scale of 1:24,000. Lucas and Anderson (1997a) stated that the Burro Canyon Formation is synonymous with Cedar Mountain Formation. The Burro Canyon Formation and Dakota Sandstone are separated by a disconformity with local erosional relief (Aubrey, 1991). The upper part of the Dakota Sandstone was deposited in coastal swamp, lagoon, and beach environments, whereas the lower part of the Dakota Sandstone and the Burro Canyon Formation were likely deposited in a fluvial environment. The combined thickness of the two formations averages 60-76 m (200-250 ft) in the mapped area. The Dakota Sandstone and Burro Canyon Formation generally serve as good foundation material, although excavations into well-cemented beds may require blasting. Where exposed in cliffs and steep hillslopes, this unit causes rockfall hazards. The unit is prone to landsliding along shale beds within the formation, especially where slope and dip are in the same direction. The Dakota Sandstone is an oil and gas reservoir in parts of the San Juan Basin. | 02.02.03 | DMU Unit 1 | Kdb | Kdb | 178-178-102 | None | DAS1 | Mostly sandstone | High | DMU1885
1889 | Jm | Morrison Formation | Morrison Formation | Upper Jurassic | In the Four Corners region, this formation includes an upper member called the Brushy Basin Member and a lower member known as the Salt Wash Member, but these were not mapped separately in this quadrangle due to poor exposures. Moreover, sandstone-rich intervals are complexly interbedded with shale in Jm within the mapped area. Throughout the mapped area, but especially where Jm beds dip in the direction of modern slopes, the unit is prone to mass wasting and is overlain by landslides and soil slips. The Brushy Basin Member and similar facies are chiefly greenish-gray, occasionally reddish-brown, bentonitic mudstone and claystone intercalated with very fine-grained sandstone and conglomeratic sandstone. It partly conformably overlies and intertongues with the Salt Wash Member (Condon, 1990) and similar sandstone facies in the mapped area. The Salt Wash Member is mainly light-gray to white, fine- to medium-grained, locally silicified, lenticular sandstone interbedded with thin beds of greenish-gray mudstone. The Salt Wash Member conformably overlies the Junction Creek Sandstone. The depositional environment of the Brushy Basin Member has been subject to debate. Condon (1990) reported it was deposited in shallow lacustrine and fluvial environments. Turner and Fishmann (1991, 2010) suggested that much of the Brushy Basin was deposited in a complex long-lived ancient, alkaline, saline lake and wetland system called Lake T'oo'dichi'. Anderson and Lucas (1997a; 1997b) stated a depositional model involving numerous smaller lakes on a vast floodplain. The Salt Wash Member and similar facies in this area were deposited in fluvial environments (Condon, 1990). Thickness of the Morrison Formation in the mapped area ranges from about 120-180 m (400-600 ft). Bentonitic beds within the formation may be prone to swelling-soil problems. The Brushy Basin Member may be subject to landsliding where exposed on steep hillslopes or on dip slopes. The Salt Wash Member has yielded large amounts of uranium in the region, although no known radioactive occurrences have been reported in the mapped area (Nelson-Moore and others, 1978). | 02.02.04 | DMU Unit 1 | Jm | Jm | 132-205-205 | None | DAS1 | Sandstone and mudstone | Medium | DMU1889
1891 | Jjc | Junction Creek Sandstone | Junction Creek Sandstone | Middle Jurassic | Light-gray to tan, highly crossbedded to massive, fine- to coarse-grained, eolian sandstone. The Junction Creek Sandstone usually is poorly exposed in the mapped area. Similar to the Entrada Sandstone, the Junction Creek Sandstone in the mapped area commonly has a distinct large-scale cross stratification. It locally forms relatively good exposures that include slickrock in lower south-facing slopes, and cliffs above timberline, but commonly is veneered by colluvium or residuum in forested areas that dominate the mapped area. It is correlative with the Bluff Sandstone in the Four Corners region and southeastern Utah (O'Sullivan, 1997; Lucas and Anderson, 1997b). It was deposited chiefly in an eolian environment (Peterson, 1972). Thickness averages about 60 m (200 ft). The J-5 regional disconformity marks the boundary between the Junction Creek-Bluff Sandstone and the underlying Wanakah Formation. It may pose rockfall hazards where exposed in steep cliffs. | 02.02.05 | DMU Unit 1 | Jjc | Jjc | 102-153-150 | None | DAS1 | Sandstone | High | DMU1891
1892 | Jw | Wanakah Formation | Wanakah Formation | Middle Jurassic | Consists of two members: an upper member composed mostly of white to tan, reddish-orange, and reddish-brown, very fine- to fine-grained sandstone and reddish-brown to greenish-gray mudstone; and the lower Pony Express Limestone Member consisting of medium- to dark-gray, very thin-bedded to laminated, micritic, oolitic, and algal limestone. The Pony Express Limestone Member locally is brecciated and fractured, and is reported to contain thin sandstone dikes that were probably injected into it from the underlying Entrada Sandstone. The formation is generally poorly exposed in the mapped area; only the Pony Express Limestone Member locally forms outcrops. The upper member of the Wanakah Formation and the Pony Express Limestone Member are probably correlative with the Summerville Formation in the Four Corners region and in part with the Todilto Formation in New Mexico. The gypsiferous part of the formation is not present in the mapped area. The Wanakah Formation conformably overlies the Entrada Sandstone. Condon (1990) suggested the upper member of the Wanakah Formation was deposited in sabkha and marginal marine environments and the Pony Express Limestone Member was of restricted marine origin. Lucas and Anderson (1997b) described the upper member (Summerville Formation) as being deposited in quiet, ephemeral shallow water on an arid coastal plain of very low slope and relief. Thickness of the upper member ranges from about 12-20 m (40-70 ft), while the Pony Express Limestone Member is about 3 m (10 ft) thick. North of Durango this member is represented by a 0.6-1.5 m (2- to 5-ft)-thick oolitic limestone (Baars and Ellingson, 1984), whereas to the south it includes a 0.6-1.5 m (5- to 15-ft)-thick limestone bed and a bed of gypsum up to about 4.6 m (15 ft) thick (Condon, 1990). The Pony Express Limestone Member hosts many replacement-type ore deposits in the La Plata Mountains. | 02.02.06 | DMU Unit 1 | Jw | Jw | 119-180-195 | None | DAS1 | Mostly mudstone | Medium | DMU1892
1910 | Jjw | Junction Creek Sandstone and Wanaka Formation, undivided | Junction Creek Sandstone and Wanaka Formation, undivided | Middle Jurassic | Mapped where poor exposures prevent recognition of the contact between the two formations. | 02.02.07 | DMU Unit 1 | Jjw | Jjw | 119-180-195 | 45° hatchure, 32-167-162, 1 pt line, 4 pt separation | DAS1 | Sandstone and mudstone | Medium | DMU1910
1893 | Je | Entrada Sandstone | Entrada Sandstone | Middle Jurassic | This unit is composed mostly of light-gray, white, or light-brown, fine- to medium-grained, highly cross-stratified quartz arenite with a calcium carbonate cement. The Entrada Sandstone in the mapped area commonly has a distinct large-scale cross stratification. It locally forms relatively good exposures that include slickrock in lower south-facing slopes, and cliffs above timberline, but commonly is veneered by colluvium or residuum in forested areas that dominate the mapped area. The Entrada Sandstone unconformably overlies the Dolores Formation and was deposited in an eolian environment. Where exposed in cliffs, the Entrada Sandstone may cause rockfall hazards. It hosts mineralized veins in the mountainous part of the quadrangle (Eckel, 1949; Neubert and others, 1992) and has yielded uranium and vanadium in the adjacent Durango West quadrangle. The Entrada Sandstone is the basal unit of the San Rafael Group in the Four Corners region. This formation was deposited as a vast erg that developed on an emergent arid coastal plain during regression of the shallow Curtis-Sundance seaway (Lucas and Anderson, 1997). The combined J-2 and J-0 regional disconformity marks the boundary between the Entrada Sandstone and the underlying Dolores Formation. Thickness ranges from 50-185 m (165-280 ft). | 02.02.08 | DMU Unit 1 | Je | Je | 32-167-162 | None | DAS1 | Sandstone | High | DMU1893
1897 | Ju | Junction Creek Sandstone, Wanakah Formation and Entrada Sandstone, undivided | Wanakah Formation and Entrada Sandstone, undivided | Middle Jurassic | Mapped in areas of poor exposures. | 02.02.09 | DMU Unit 1 | Ju | Ju | 119-180-195 | 135° hatchure, 102-153-150, 1 pt line, 4 pt separation + 45° hatchure, 32-167-162 1 pt line, 4 pt separation | DAS1 | Sandstone and mudstone | Medium | DMU1897
1894 | TRd | Dolores Formation | Dolores Formation | Upper Triassic | The Dolores Formation is mostly reddish-brown sandstone, shale, and siltstone; light-brown, gray, and reddish-brown lenticular sandstone; and limestone-pebble conglomerate containing rare thin limestone beds. The upper part includes massive pedoturbated red mudstone beds, locally well exposed just below the sharp unconformable contact with overlying Je, as along roadcuts of the main access road in the Monument Hill quadrangle along the southwest slope of Sliderock Mountain. The very well sorted fine-grained sandstone forming thin cross bed sets 1 m or less in thickness suggest a depositional environment of sheet sands proximal to ephemeral fluvial conditions in an arid setting. The limestone pebble clasts may have been reworked from calcic soils documented within the Dolores Formation in the southwest Colorado region. The formation is locally well exposed on steep hillslopes, but typically it is partly to completely covered. Lucas and others (1997b) correlated the Dolores Formation with an upper member (Rock Point Formation) and lower member (Moss Back Formation) of the Chinle Group strata on the Colorado Plateau. Conglomerate of the Dolores Formation in the mapped area is clast and matrix supported and contain abundant subrounded to angular fragments of limestone in a sandy to carbonate-rich matrix. The conglomerate is reported to locally contain teeth and bone fragments from crocodilians. The limestone-pebble conglomerate locally forms prominent cliffs. The Dolores Formation was deposited in arid fluvial, flood plain, with marginal sheet sand and lacustrine environments (Condon, 1990). Thickness in the mapped area is variable ranging from 150-250 m (500-820 ft). The Dolores Formation unconformably overlies the Cutler Formation. Although the contact between the Dolores and Cutler is a major unconformity, it is not easily recognizable even where exposures are good. In the Durango, area Kirkham and others (1999) placed the contact at the base of the first limestone-pebble conglomerate that occurred stratigraphically above the highest arkosic bed in the Cutler Formation. The Dolores Formation may be prone to rockfall hazards where exposed in steep cliffs. | 02.02.10 | DMU Unit 1 | ^d | TRd | 0-132-168 | None | DAS1 | Sandstone and mudstone | Medium | DMU1894
1895 | Pc | Cutler Formation | Cutler Formation | Lower Permian | The Cutler Formation in the mapped area is composed of interbedded clastic sedimentary rocks ranging in color from medium- to dark-reddish brown, grayish brown, purplish red brown, and maroon. This unit is composed mostly of interbedded sandstone, feldspathic sandstone, arkosic conglomerate, and thin-bedded to thinly laminated shale and siltstone. Siltstones and shales in the Cutler Formation are characterized by bluish-green to grayish-green reduction spots up to at least 5 cm (2 in) in diameter. Sandstones are immature to submature and contain relatively high concentrations of quartz, potassium feldspar, and biotite in a hematitic cement. Beds of conglomerate are dominated by subangular to subrounded granule- to pebble-sized clasts of quartz, quartz arenite, granite, biotite gneiss, and arkosic sandstone. Bedding in this unit is thin to very thick with alternating ledges and slopes. Sandstone and conglomerate beds typically have a pronounced low-angle, tangential to trough- cross-stratification. Siltstones are mostly thin bedded to thickly laminated, and weathered surfaces are broken into thin slabs in most outcrops. The Cutler Formation was deposited in fluvial and alluvial-fan environments in the Paradox Basin during erosion of the adjacent Uncompaghre uplift of the Ancestral Rocky Mountains to the north of this area (Campbell, 1979, 1980). Within the mapping area the Cutler Formation ranges in thickness from 460-650 m (1500-2100 ft). This unit may be prone to rockfall hazards where exposed in steep cliffs. | 02.02.11 | DMU Unit 1 | Pc | Pc | 115-178-255 | None | DAS1 | Sandstone and mudstone | Medium | DMU1895
1896 | Ph | Hermosa Group | Hermosa Group | Middle Pennsylvanian | Outcrops of the Hermosa Group in the northeast part of the mapped area along Hermosa Creek form some of the most southern exposures of Pennsylvanian strata on the eastern side of the Paradox Basin. On the basis of its brachiopod faunas, the Hermosa Group was assigned a Desmoinesian age (refer to Franczyk and others, 1995). The Hermosa Group in the mapped area was subdivided into a lower Pinkerton Trail Formation and an overlying undifferentiated part by Franczyk and others (1995). They interpret four different carbonate lithofacies in the Hermosa Group that represent various marine depositional environments. These lithofacies were established based on mineral assemblages, textures and structures, biotic assemblages, and inferred depositional environments. In the undifferentiated part of the Hermosa Group there are stacked carbonate-clastic depositional cycles which are dominated by carbonate units at the base and grade upward into coarsening clastic cycles. These cyclic deposits formed in marine deltaic and nonmarine deltaic and alluvial systems. Lithofacies 1 corresponds to the Pinkerton Trail Formation. It is dominated by a succession of thin- to thick-bedded calcareous black shale, wackestone, packstone, rare grainstone and dolomitic limestone. Carbonate lithologies in this formation contain crinoid stems, brachiopod shells and spines, fusulinids, monaxon sponge spicules, and bryozoa (Franczyk and others, 1995). Carbonate lithofacies in the undifferentiated part of the Hermosa Group above the Pinkerton Trail Formation are thin to thick bedded and contain dolostone, dolomitic limestone, calcareous shale, dolomitic siltstone, calcareous shale with about 40% limestone pebbles and cobbles, fossiliferous limestone, limey mudstone, packstone, grainstone, and wackestone. Faunal assemblages noted by Franczyk and others (1995) in these lithofacies include crinoid columns, echinoderm plates, brachiopod shells and spines, algal laminations, stromatolitic structures, fusilinids, foraminifera, phylloid algae, ostracods, monaxon sponge spicules, gastropods, and pelecypods. Clastic deposits in the stacked successions include very thin to very thick beds of mudstone that locally contain organic debris, siltstone, fine- to coarse-grained sandstone, and pebbly conglomerate. These beds vary from massive to cross stratified. Siltstones and sandstones observed during this study ranged from mature quartz arenites to immature micaceous siltstones. Detrital minerals include quartz, feldspar, mica, glauconite, and fossil fragments (Franczyk and others, 1995). Rock fragments in pebbly sandstones and conglomerates include milky quartz, very fine-grained black to green shale, amphibolitic and granitic gneiss, granite, gray limestone, brown to tan quartzite, and gray to brown chert. Sandstone beds locally contain slender fragments of carbonized material up to 10 cm (4 in) in length that are interpreted as fossilized flora. There are also worm burrows in many sandstone layers. Lithofacies 2 of Franczyk and others (1995) makes up part of the undifferentiated part of the Hermosa Group, which includes gypsum beds, dolomitic mudstone, black shale, conglomerate and claystone. The conglomerate has a reddish- to orangish-brown matrix of siltstone and fine-grained sandstone. It contains subangular to angular pebble- to cobble-sized clasts of red to maroon, medium-grained sandstone, brown siltstone, brownish iron-stained medium-grained calcareous sandstone, and grayish-black limestone. About 450 m (1500 ft) of the uppermost part of the Hermosa Group are exposed in the mapped area (northeast corner); the base of the group is not exposed, but is reported to exceed 760 m (2000 ft) in thickness nearby. | 02.02.12 | DMU Unit 1 | Ph | Ph | 190-210-255 | None | DAS1 | Sandstone and mudstone | Medium | DMU1896

#### Glossary

OBJECTID | Term | Definition | DefinitionSourceID | Glossary_ID
--- | --- | --- | --- | ---
182 | bed | (a) An informal term for strata that are incompletely known, constitute a lithologically similar succession, or are of economic significance. (b) A formal stratigraphic unit consisting of several continuous strata of similar lithology | AGI | GLO182
12 | Boundary | A line that marks the limits of an area | DICT | GLO12
1 | certain | Identity of a feature can be determined using relevant observations and scientific judgment; therefore, one can be reasonably confident in the credibility of this interpretation. | FGDC-STD-013-2006 | GLO1
17 | contact | A plane or irregular surface between two types or ages of rock; examples are faults, intrusive borders, bedding planes separating distinct strata, and unconformities. (b) The surface between two fluids in a reservoir, i.e. oil and gas, oil and water, or gas and water. Syn: interface. adj. Said of a mineral deposit that occurs at the contact of two unlike rock types. | AGI | GLO17
179 | dike | A tabular igneous intrusion that cuts across the bedding or foliation of the country rock. | AGI | GLO179
21 | DMU-Heading1 | GeMS hierarchy formatting term | GeMS | GLO21
22 | DMU-Heading2 | GeMS hierarchy formatting term | GeMS | GLO22
207 | DMU-Heading3 | GeMS hierarchy formatting term | GeMS | GLO207
23 | DMU Unit 1 | GeMS hierarchy formatting term | GeMS | GLO23
177 | DMU Unit 1 (1st after heading) | GeMS hierarchy formatting term | GeMS | GLO177
27 | fault | A discrete surface or zone of discrete surfaces separating two rock masses across which one mass has slid past the other. Cf: shear zone; fault zone . | AGI | GLO27
61 | High | unusual or considerable in degree, power, intensity, etc. | DICT | GLO61
188 | Horizontal beds | The orientation of a structural element (plane or line) relative to a horizontal plane. Attitudes of planes are expressed by strike and dip (or dip direction and dip), whereas attitudes of lines are expressed by bearing (or trend, azimuth) and plunge. In this case the dip is horizontal. | AGI | GLO188
190 | lateral moraine crest | The highest point of (a) a low ridgelike moraine carried on, or deposited at or near, the side margin of a mountain glacier. It is composed chiefly of rock fragments loosened from the valley walls by glacial abrasion and plucking, or fallen onto the ice from the bordering slopes. (b) An end moraine built along the side margin of a glacial lobe occupying a valley. | AGI | GLO190
62 | Medium | something intermediate in nature or degree | DICT | GLO62
208 | monocline lower hinge | The locus of maximum curvature or bending in a folded surface, usually a line | AGI | GLO208
184 | moraine crest | The highest point of a mound, ridge, or other distinct accumulaion of unsorted, unstratified glacial drift, predominantly till, deposited chiefly by direct action of glacier ice, in a variety of topographic landforms that are independent of control by the surface on which the drift lies. | AGI|DAS1 | GLO184
2 | questionable | Identity of a feature cannot be determined using relevant observations and scientific judgment; therefore, one cannot be reasonably confident in the credibility of this interpretation. For example, IdentityConfidence = questionable is appropriate when a geologist reasons "I can see some kind of planar feature that separates map units in this outcrop, but I cannot be certain if it is a contact or a fault." | FGDC-STD-013-2006 | GLO2
206 | sill | A tabular igneous intrusion that parallels the bedding or foliation of the sedimentary or metamorphic country rock, respectively. | AGI | GLO206
185 | Strike and dip of beds | The orientation of a structural element (plane or line) relative to a horizontal plane. Attitudes of planes are expressed by strike and dip (or dip direction and dip), whereas attitudes of lines are expressed by bearing (or trend, azimuth) and plunge. | AGI | GLO185
187 | vein | Any fracture that contains mineralized material. Veins can display either crack-normal extension or shear displacement coupled with crack-normal extension. | AGI | GLO187

#### MiscellaneousMapInformation

OBJECTID | MapProperty | MapPropertyValue | MiscellaneousMapInformation_ID
--- | --- | --- | ---
1 | DOI | https://doi.org/10.58783/cgs.2508.fnss5751 | MMI1
2 | OFR | OF-25-08 | MMI2
3 | AUTHORS | SCOTT LUNDSTROM, DAVID GONZALES, JACOB LONGRIDGE, AND MIKE O'KEEFFE | MMI3
4 | TITLE | DIGITAL GEOLOGIC MAP DATABASE OF THE LA PLATA MOUNTAIN MAP AREA LA PLATA, MONUMENT HILL, RAMPART HILLS, AND THOMPSON PARK QUADRANGLES LA PLATA AND MONTEZUMA COUNTIES, COLORADO | MMI4
5 | PUBLICATION YEAR | 2026 | MMI5
6 | LiDAR-Topo discrepancy | Much of the geologic mapping benefitted from Lidar surfaces. The base map is derived from a 10m DEM. The discrepancy between the LiDAR and topo is evident in some areas, but the geology is accurate. | MMI6
7 | ACKNOWLEDGMENTS | This geologic mapping was funded by the U.S. Geological Survey through the Earth MRI program, a critical minerals initiative, and by the Colorado Geological Survey (CGS), including support from the Severance Tax Operational Fund, which is derived from taxes on the extraction of nonrenewable natural resources. GIS transformation and editing into a GeMS formatted geodatabase and the associated pdf layout were completed by Pangaea Geospatial, Gunnison, Colorado. Steve Cumella, Nathan Rogers and Alex Marr provided valuable discussions in the field. Our geologic perspectives were broadened and improved by discussion and consideration of geologic observations with Metallic Minerals staff, including Scott Petzel, and Jeff Cary. Reviews by Steve Cumella and Matt Morgan also resulted in substantial improvements. | MMI7
8 | OF number-Pub Year | Although assigned an OFR number in 2025, this report was published in 2026. | MMI8
9 | AUTHOR AFFILIATION1 | Scott Lundstrom, Mike O'Keeffe, Colorado Geological Survey, Colorado School of Mines, Golden, Colorado | MMI9
10 | AUTHOR AFFILIATION2 | David Gonzales, Department of Geosciences, Fort Lewis College, Durango, Colorado | MMI10
11 | AUTHOR AFFILIATION3 | Jacob Longridge, Metallic Minerals, Vancouver, British Columbia | MMI11
13 | FUNDING | This mapping project was funded jointly by the Colorado Geological Survey and the U.S. Geological Survey through the Earth MRI mapping program under ERMI agreement number G22AS00001. | MMI13
14 | 1 ADDITIONAL TEXT | The geodatabase herein provides the geologic mapping of the four quadrangle area spanning most of the La Plata Mountains (LPM). The LPM are a mineralized Laramide igneous intrusive complex situated on the southwest margin of the San Juan Mountains and spanning the geomorphic and stratigraphic transitions between the San Juan Mountains and the Colorado Plateau. The LPM mapped area is largely within lands managed by the San Juan National Forest plus private inholdings of patented mining claims, and more extensive private land including rangeland of Thompson Park and the lower Mancos River valleys, parcels owned and managed by the southern Ute Nation, and adjoining public land managed by BLM and the State of Colorado. The mapped area covers four 7.5-minute quadrangles including the central La Plata 7.5-minute quadrangle which includes all of the highest peaks of LPM, flanked by Rampart Hills quadrangle on the west, Monument Hill quadrangle on the east and Thompson Park quadrangle on the southwest. This L-shaped mapped area adjoins quadrangles previously mapped by the Colorado Geological Survey including Hesperus, Durango West, and Hermosa. Within the mapped area, the highest peaks, largely above tree line, are connected to form a roughly horseshoe-shaped range around the uppermost La Plata River basin. The range also includes major ridges that connect to Hesperus Peak to the west, the high point of the range; Jackson Ridge, Helmet Mountain, and Red Arrow Dome on the southwest; Burro Mountain on the northwest; Indian Trail Ridge on the north; and Monument Hill on the east. These peaks and ridges form the headwater drainage basins of the East, West, and Middle Mancos Rivers, the La Plata River basin, and headwater areas of Bear Creek, South Fork Hermosa Creek, Junction Creek, Lightner Creek and Cherry Creek that flank the range on the north, east and southwest. The upper parts of each of these basins were glaciated during the Late Pleistocene, with the most extensive paleoglaciers in the Bear Creek and La Plata basins. | MMI14
15 | 2 ADDITIONAL TEXT | This geologic mapping and characterization was funded by the U.S. Geological Survey (USGS) through the Earth MRI program, a critical minerals initiative, and by the Colorado Geological Survey (CGS), including support from the Severance Tax Operational Fund, which is derived from taxes on the extraction of nonrenewable natural resources (metallic minerals, molybdenum, oil and gas, oil shale, and coal). This geologic mapping provides regional geologic context that complements previous and ongoing exploration for mineral resources, including copper, precious metals, and platinum-group elements. Recently acquired LiDAR data for the mapped area, combined with field work and other geospatial datasets (including NAIP imagery and USGS digital data), substantially improved the recognition and location of geologic features relative to the work of Eckel (1949), which was based on much older topographic mapping. Additional contributions include petrographic work by David Gonzales, whole-rock geochemistry, and new geochronologic analyses, including Re-Os, U-Pb, and Ar-Ar data. Ar-Ar analyses were conducted by Dan Miggins (Oregon State University), U-Pb zircon analyses by Mark Schmitz (Boise State University), and Re-Os analyses by Holly Stein (AIRIE). The sedimentary bedrock record exposed at the surface spans Pennsylvanian to late-Cretaceous time and includes the following formations: Cutler, Dolores (Chinle), Entrada Sandstone, Wanakah, Junction Creek Sandstone, Morrison, Dakota/Burro Canyon, Mancos Shale, and formations of the Mesaverde Group, including the Point Lookout Sandstone, Menefee Formation, and the Cliffhouse Sandstone. The undivided Hermosa Group is also present. The mapped area spans facies changes and major unconformities, but various types of alteration, forest soils, colluvium, and alpine Quaternary cover challenge such characterization. | MMI15
16 | 3 ADDITIONAL TEXT | The igneous record, largely mapped and well-characterized by David Gonzales in the central core area, is entirely intrusive, and all new (including Re-Os dates) and previous geochronology indicate Laramide (latest Cretaceous) ages for the dominant central stocks, extensive sills and connecting dikes. The igneous rocks are potassic alkaline to calk-alkaline (largely quartz-poor) and include lamprophyre (gabbro), diorite, granodiorite, monzonite, and syenite. Exposed relations and geochronology do not indicate that sills largely preceded central stocks, in contrast to the interpretations of Cross et al. (1899) and Eckel (1949). Gentle folds and local limited-displacement faulting (generally less than 10 m) are superimposed on a general southwestward homoclinal trend in which the oldest bedrock strata are exposed in the northeast corner of the mapped area and youngest pre-Quaternary rocks are exposed in the southwest corner, at the south end of the Thompson Park quadrangle. The emplacement of central stocks and many sills contributed to a general doming of strata centered over the upper La Plata River basin along with monoclinal flexures which are down to the west over the upper East Mancos River basin and flanking the central core stock, and southward on the south flank of the range toward the San Juan Basin. The southwest flank of the range is partly connected to a smaller domal structure through which the middle part of the East Mancos River has cut a canyon flanked by Red Arrow mine area on the north and Caviness Mountain on the south. These flanking structures and associated upland ridges are cut and perhaps structurally augmented by steep faults of various orientations and senses of movement. Dominant fault trends are northwest trending to east-west trending on the south to southwest flank of the range, commonly with south-side-down senses of displacement. Some of these are only suggested faults manifested as linear scarps trending obliquely across the steep slope of the range flank. Northeast-striking high-angle faults cut across the northern part of the area including Indian Trail Ridge and adjoining areas to the east. | MMI16
17 | 4 ADDITIONAL TEXT | Hydrothermal, telluride-rich, precious-metal and base-metal mineralization accompanied or followed Laramide igneous activity in the La Plata Mountains. Hydrothermal fluids migrated into fractures and favorable stratigraphic horizons, contributing to mineralization and alteration. Eight distinct types of mineralization are recognized (Galbraith, 1941; Eckel, 1933, 1936, 1949; Eckel et al., 1968; Saunder and May, 1986; Cappa, 1998) with important production coming from quartz-telluride veins, quartz-gold-sulfide veins, and Ag-Au replacement deposits. The epithermal alkaline deposits of the La Plata district are the oldest of a series of alkaline deposits that developed from Wyoming to Mexico on a regional trend that roughly parallels the Rio Grande rift system and the region commonly referred to as the Colorado Mineral Belt (e.g., Kelley and Ludington, 2002). Quaternary mapping includes 25 map units of Pleistocene and Holocene (postglacial) age in this steep lofty range (peak elevations ranging from ~12,000 to >13,200 ft) which is on the southwest windward position with respect to the San Juan Mountains. Previous mapping by Eckel (1949) and Cross et al. (1899) emphasized bedrock and did not include Quaternary units except for one landslide area. We recognize and map multiple ages and grades of terrace outwash and alluvium in the south and west parts of the mapped area (basins of Mancos River and Cherry Creek), likely spanning pre-Bull Lake to modern age. The glacial record in the mapped area is dominated by deposits of the Late Pleistocene (Pinedale) including full glacial and recessional lateral moraines, and patchy discontinuous till cover among glacial erosional forms on steep slopes and glacial valleys. The record also includes laterally ponded local basins that adjoin maximum glacial extent in Bear Creek and south Hermosa Creek. Extensive areas of landsliding are mapped (locally multiple ages and crosscutting sets), especially in the western area underlain by Mancos Shale, both within and outside glacial limit. Extensive and varied postglacial Holocene deposits include active and relict rock glaciers, talus in alpine areas, steep forested colluvial soils, and alluviated valley bottoms. | MMI17

### Database Inventory

This summary of database content is provided as a convenience to GIS analysts, reviewers, and others. It is not part of the GeMS compliance criteria.
DataSources, nonspatial table, 11 rows
DescriptionOfMapUnits, nonspatial table, 65 rows
GeoMaterialDict, nonspatial table, 101 rows
Glossary, nonspatial table, 21 rows
MiscellaneousMapInformation, nonspatial table, 16 rows
GeologicMap, feature dataset
MapUnitPolys, simple polygon feature class, 1726 rows
DataSourcePolys, simple polygon feature class, 4 rows
ContactsAndFaults, simple polyline feature class, 6710 rows
OrientationPoints, simple point feature class, 92 rows
GeologicLines, simple polyline feature class, 233 rows
MapUnitLines, simple polyline feature class, 524 rows
FaultMovementAnno, annotation polygon feature class, 38 rows
GeologicMap_topology, topology