GeMS validation of OF-23-04_Milton_Reservoir.gdb

File written by GeMS_ValidateDatabase.py, version of 5/15/2024
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Database path: C:\Projects\OF-23-04_Milton_Reservoir\OF-23-04_Milton_Reservoir-Publication\OF-23-04_Milton_Reservoir-Database\OF-23-04_Milton_Reservoir.gdb
Output directory: C:\Projects\OF-23-04_Milton_Reservoir
Metadata file: None
Check embedded metadata: False
Skip topology check: False
Refresh GeoMaterialDict: False
Delete extra rows in Glossary and DataSources: False
Compact GDB: True

This database is LEVEL 3 COMPLIANT.

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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: 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


GenericPoints, Well_API
GenericPoints, Facility_Name
GeochronPoints, SampleDepth
GeochronPoints, DateCollected
GeochronPoints, Delta13C
GeochronPoints, MeasuredRadiocarbonAge
GeochronPoints, CalibratedAge
GeochronPoints, Aliquots
GeochronPoints, GrainSize
GeochronPoints, CentralMinAgeModel
GeochronPoints, Overdispersion
GeochronPoints, U_PPM
GeochronPoints, Th_PPM
GeochronPoints, K2O_PCT
GeochronPoints, CosmicDoseRate
GeochronPoints, DoseRate
GeochronPoints, SAR_OSL_Age
GeochronPoints, Latitude
GeochronPoints, Longitude
GeochronPoints, Aliquot
GeochronPoints, H2O_PCT
CMUMapUnitPolys, IdentityConfidence
CMUMapUnitPolys, DataSourceID

Tables


CorrelationOfMapUnits
CrossSectionA
CrossSectionB
GenericPoints
GeochronPointsAnno
MapUnitPolysAnno
GenericPointsAnno
CMULinesAnno
CMUMapUnitPolysAnno
CSA_CartoLines
CSA_CartoLinesAnno
CSA_DHCollar
CSA_DHTrace
CSA_DHCollarAnno
CSAMapUnitPolysAnno
CSB_DHTrace
CSB_CartoLines
CSB_CartoLinesAnno
CSB_DHCollar
CSB_DHCollarAnno
CSBMapUnitPolysAnno

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

MapUnit DescriptionOfMapUnits GeologicMap CrossSectionA CrossSectionB CorrelationOfMapUnits
PeKd X X -- -- X
Qe X X -- -- X
Qg X X -- X X
Bedrock X -- -- X --
Kn X -- X -- X
Qg4 X X -- -- X
Qu X -- X -- --
Kfh X -- X -- X
Qa X X -- X X
Kd X -- X -- X
Kl X X X -- X
Qg3 X X -- -- X
Qes X X -- X X
Kp X -- X -- X
af X X -- -- X
water X X -- -- --
Kcgg X -- X -- X

Contents of Nonspatial Tables

DataSources

OBJECTIDSourceNotesURLDataSources_ID
2This studyNoneNoneDAS1
9Online dictionaryNonehttps://dictionary.com/DICT1
1Federal 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.Nonehttps://ngmdb.usgs.gov/fgdc_gds/geolsymstd.phpFGDC-STD-013-2006
6GeMS standardNonehttps://ngmdb.usgs.gov/Info/standards/GeMS/GeMS1
8Klaus K.E. Neuendorf, James P. Mehl, Jr., and Julia A. Jackson, 2011, Glossary of Geology, Fifth Edition. Published by American Geosciences Institute. ISBN 978-0-922152-92-6.Nonehttps://www.americangeosciences.org/pubs/glossaryGEODICT1

DescriptionOfMapUnits

OBJECTIDMapUnitNameFullNameAgeDescriptionHierarchyKeyParagraphStyleLabelSymbolAreaFillRGBAreaFillPatternDescriptionDescriptionSourceIDGeoMaterialGeoMaterialConfidenceDescriptionOfMapUnits_ID
21NoneDESCRIPTION OF MAP UNITSDESCRIPTION OF MAP UNITSNoneNone01DMUHeading1DESCRIPTION OF MAP UNITSNoneNoneNoneDAS1NoneNoneDMU01
23NoneDMU descriptionDMU descriptionNoneA summary of the mineral resources, groundwater resources, geologic hazards, and geologic history within the quadrangle can be found in Plate 2. Division of geologic time follows the International Chronostratigraphic Chart (International Union of Geological Sciences, 2022). For particle size categories, refer to the Udden-Wentworth grain-size scale (in Nichols, 2009). Descriptions of secondary calcium carbonate (calcic) soil development and soil colors are based on Machette (1985) and Munsell Color (1991), respectively. The type of effervescence in sediment or soil observed when treated with dilute hydrochloric acid is according to U.S. Department of Agriculture (2018).01-01DMUUnit1DMU descriptionNoneNoneNoneDAS1NoneNoneDMU02
14NoneSURFICIAL DEPOSITSSURFICIAL DEPOSITSNoneNone02DMUHeading1SURFICIAL DEPOSITSNoneNoneNoneDAS1NoneNoneDMU03
15NoneHUMAN-MADE DEPOSITSHUMAN-MADE DEPOSITSNoneNone02-01DMUHeading2HUMAN-MADE DEPOSITSNoneNoneNoneDAS1NoneNoneDMU04
1afArtificial FillArtificial Filluppermost HoloceneArtificial fill (Uppermost Holocene) — Mostly riprap, fill material, refuse, and engineered soil used in the construction of roads, buildings, dams, and landfills. Material is generally made up of unsorted clay, silt, sand, and rock fragments. The unit is typically less than 6 m in thickness. Artificial fill may be subject to slumping, settlement, and erosion if not adequately compacted.02-01-01DMUUnit1afaf255-255-255NoneDAS1"Made" or human-engineered landHighDMU05
16NoneEOLIAN DEPOSITSEOLIAN DEPOSITSNoneNone02-02DMUHeading2EOLIAN DEPOSITSNoneNoneNoneDAS1NoneNoneDMU06
22QesEolian sandEolian sandHoloceneEolian sand (Holocene) — Light brown to yellowish brown (10YR), massive, loose to moderately stiff, moderately to well sorted, fine to coarse sand with trace to minor percentage (< 15%) of very coarse sand, silt and clay, and gravel ranging from granules to 5-mm pebbles. Sand grains are subrounded to rounded, and sand composition is 75-85% quartz, 15-20% feldspar, and trace to 7% opaque minerals. The sand does not effervesce when treated with dilute hydrochloric acid (HCl). This unit covers more than 80% of the quadrangle. According to geotechnical borehole and water well logs, unit Qes thickness is as great as 9 m. The sediment of Qes is likely derived from wind erosion of the alluvium from the South Platte River and its tributaries, and residuum of Upper Cretaceous rocks (Muhs and others, 1999; Madole and others, 2005). Unit Qes may locally contain higher silt and clay content at some of the locations where it is near the contact with the bedrock or valley-fill sediments (unit Qa). Sand content of unit Qes in the northern part of the Milton Reservoir quadrangle is greater than in the southern part. Multiple sieve analyses were performed on this unit near Beebe Draw Farms in the northern part of the quadrangle. O’Keeffe and others (2018) reported a sand content of 97.4% and a fines (silt and clay) content of 2.6%. Horizon Construction Service (2000) reported two layers of Qes in the same area. In the upper layer (0.9-2.1 m below ground surface) the sand content is 78-98% and the fines content is 2-22%. The lower layer (2.1-4.3 m below ground surface) has a higher but more variable fines content of 6-64%. During the field work for this map, an exposure possibly corresponding to the lower layer as noted by Horizon Construction Service (2000), was found in an oil facility pit near Beebe Draw Farms, where the fines-rich (silt and clay) sand is pale brown and is fine to coarse grained. Four samples were collected in unit Qes for optically stimulated luminescence (OSL) dating. Age estimates range from 3,305 ± 135 SAR-OSL yrs to 6,395 ± 310 SAR-OSL yrs (see sample locations on Plate 1 geologic map and Table 2 on Plate 2 for specific sample data). Within the quadrangle, Madole (1995) obtained an OSL age estimate of 3,230 ± 250 SAR-OSL yrs on a dune southwest of the Weld County Road (WCR) 32 and WCR 35 junction. Madole and others (2005) also obtained an OSL age estimate of 4,100 ± 1,300 SAR-OSL yrs in this same unit in the Milton Reservoir quadrangle but did not include a specific location. Other Qes dates from surrounding quadrangles include 3,165 ± 290 SAR-OSL yrs in Valley View School (Keller and Marr, 2023), and 9,350 ± 40 and 8,440 ± 30 14C yrs BP in La Salle (Palkovic and others, 2019). Northwest of Milton Reservoir, along the Platte Valley Canal, a possible interdune deposit underlies the loose dune sand of unit Qes. The sediment is made up of layers of reddish-brown, 1’s of centimeter-scaled, discontinuous fine to coarse sand, that is interbedded with looser sand layers, which weather to a corrugated appearance where exposed. While the grain size distributions of the layers are similar, the reddish-brown layers have slightly more resistance to weathering that is likely due to cementation from iron-oxide precipitate. From the northwest Milton Reservoir shore, this deposit was exposed to the northwest for about 1 km to where Beebe Draw Parkway crosses the Platte Valley Canal. The nature of this sedimentological feature may be attributed to an interdunal feature called adhesion structures. These structures are formed in pulses, possibly seasonal or after precipitation events, when dry windblown sand sticks to a damp surface (Kocurek, 1981). Two age estimates were obtained from this possible interdune sediment. A bulk 14C sample (MR052C14) at the Beebe Draw Parkway bridge over the Platte Valley Canal yielded a date of 400 ± 30 yrs BP; and an OSL sample (OSL-MRAM-3) at the Milton Reservoir shore yielded an age estimate of 6,395 ± 310 SAR-OSL yrs. In addition, an OSL sample (OSL-MRAM-4) of the overlying dune sand at the contact of the interdune deposit yielded an age estimate of 4,845 ± 235 SAR-OSL yrs (See sample dating Tables 1 and 2 on Plate 2). Longitudinal and parabolic dune landforms overprint the Milton Reservoir quadrangle landscape. The dune crests indicate that the prevailing wind direction is from the northwest. Blowout features from wind erosion are common in the dunes, but are now mostly covered by vegetation, indicating that dune migration is currently limited. The dunes in the northern part of the quadrangle are larger in area and appear to coalesce whereas dunes in the middle and southern parts are smaller in area and are more scattered. In areas where there is sparse vegetation, unit Qes can be susceptible to wind erosion and dune migration. Depending on silt and clay content, sediment void space, and clay mineralogy, the deposit may be prone to expansive or collapsible soil properties when wetted, characteristics which could impact future and existing buildings and infrastructure. Unit Qes is a potential source of borrow material.02-02-01DMUUnit1QesNone255-247-153NoneDAS1Dune sandHighDMU07
6QeEolian sedimentEolian sedimentHolocene and upper PleistoceneEolian sediment (Holocene and Upper Pleistocene) — Brown and light brownish yellow (10 YR), sandy silty clay or clayey silt. The sand grains are subangular to subrounded and range from very fine to medium. Unit Qe unit tends to be cohesive and form hard surfaces when dry but locally contains loose silt layers. The unit occurs in interdunal valleys and is locally covered by surficial sheets of sand. In other locations in the Colorado Piedmont, unit Qe’s age ranges from about 2,000 to 10,000 yrs BP (Keller, 2023) but at one location in the nearby Johnstown quadrangle, unit Qe is as old as 21,000 SAR-OSL yrs (Palkovic and Morgan, 2017). At the junction of WCR 20 and WCR 38 a soil with a Bt/Bk profile was exposed in a 2.4-m deep silage pit. The soil profile, from top to bottom, consists of: 0.6 m of topsoil (possibly A and Bt horizons) reworked by eolian activity; Bt horizon with white and purple colored mottles 0.2 m thick; and a Bk horizon 1.2 m thick that has developed a 0.8-m thick Stage II calcic soil with secondary veinlets (< 1 mm to 1 mm) and nodules from < 1 mm to 1 cm in diameter. The Bk horizon developed over a layer of fine to medium loose sand that has 0.3 m of vertical exposure. On the basis of this soil-profile morphology, the relative age of the sediment at the silage pit is likely Late Pleistocene (Ralph Shroba, personal commun, 2024; Kellogg and others, 2008). Soil formed in eolian sediment covered by 1-1.5 m of sand was observed in the northeast boundary of the Hudson quadrangle (Forman and Maat, 1990). The latter used thermoluminescence analysis to date the buried soil and radiocarbon analysis to date the overlying sand at their contact. The age results were 8,800 ±1,700 yrs BP and 8,600 ±1,300 yrs BP for the soil, and 7,270 ±110 14C yrs BP and 8,280 ±150 14C yrs BP for the overlying sand. The mapping of unit Qe was delineated based on lidar imagery and geologic maps of the adjacent Hudson and Platteville quadrangles (Soister, 1965b; 1965c). During this investigation, unit Qe was observed near the Milton Reservoir and Hudson quadrangle boundary mainly through digging ~0.3 m deep sample holes to determine the sedimentological characteristics of the unit. This unit was not observed at the northwest boundary adjacent to the Platteville quadrangle due to lack of exposure and being covered by sand. According to Soister (1965b; 1965c), the unit Qe is a sandy clayey silt with some silty fine sand and local isolated gravel possibly from reworked upland gravel deposits. The unit Qe on the Platteville quadrangle includes multiple loess sheets with Bt and Bk soil horizons and underlies most of the sandy eolian units. These multiple loess sheets are likely of Pleistocene age. Unit thickness in the Platteville and Hudson quadrangles is generally 0.9-4.6 m but can locally be as thick as 7.6 m. Unit Qe is a potential source of borrow material and may be prone to swelling and soil settlement (hydrocompaction), depending on its percentage of fines, clay mineralogy, and moisture content.02-02-02DMUUnit1QeQe255-252-223NoneDAS1Eolian sedimentMediumDMU08
17NoneALLUVIAL DEPOSITSALLUVIAL DEPOSITSNoneNone02-03DMUHeading2ALLUVIAL DEPOSITSNoneNoneNoneDAS1NoneNoneDMU09
2QaAlluviumAlluviumHolocene and upper PleistoceneAlluvium, Undivided (Holocene and upper Pleistocene) — Unit Qa comprises the upper portion of the Beebe Draw valley-fill sequence and overlies the ancestral South Platte gravel deposits (unit Qg). This unit can be inferred from water well driller’s logs obtained from the Colorado Division of Water Resources (CO DWR, 2022) throughout Beebe Draw and was observed also by Smith and others (1964), Robson (1996), and Robson and others (2000). As depicted on cross section B-B’, the thickness of unit Qa is 1.5-13 m. In the Milton Reservoir quadrangle, most of the deposit on the surface of Beebe Draw is covered and intermixed with eolian deposits. Because of its low surface relief, unit Qa was mapped by using a 2-ft contour topographic map generated from a 1-m pixel lidar digital elevation model. Polygons of valley-fill sediment from sand and gravel reports of Schwochow and others (1974) were also used to help delineate unit Qa. This unit was exposed at a borrow pit for the Steve Sharp Crane and Rigging building at the junction of WCR 41 and WCR 24. At the pit, two stratigraphic sections of Qa revealed lateral variability in the deposit. On the west side (near MR037BC14 sample shown on the Plate 1 geologic map), the upper 0.5 m of a 1.1-m pit face is composed of brown silty clay or clayey silt and has carbonate nodules up to 3 mm in diameter. The underlying 0.5-1.1 m section is composed of very pale brown (10 YR), moderately to well sorted, loose, stratified, fine to medium sand with minor coarse and very coarse sand. The layer also has bedding at the 1’s of millimeter to 1’s of centimeter scale. At 0.5-m depth is a bed of granules and very coarse sand. There is no visible secondary calcium carbonate in the sand. Sand composition is about 75% quartz, 15% feldspar and others, and 10% opaques. However, on the southwest side of pit (near sample MR037CC14 shown on the map on Plate 1) is a 1.8-m face where the top 0.4 m is disturbed material from past operations and farming. The underlying 0.4-1.8 m section is light yellowish brown (10 YR), silty clay or clayey silt with only minor fine sand; the coarse sand and granules noted in the west side are absent. The unit has a weakly developed Bk calcic soil horizon about 0.3 m thick. Unit Qa is also mapped with lithological variations along Beebe Draw in the La Salle quadrangle to the north (Palkovic and others, 2019) and in the Hudson quadrangle to the south (Soister, 1965b). In the Steve Sharp Crane and Rigging borrow pit, the deposit that includes sample MR037CC14 is truncated to the east against the underlying unit Qg. The deposit with sample MR037BC14 has a channel shape and appears to dip to the east and truncates and overlays the unit with sample MR037CC14 to the south. This stratigraphic relationship is supported by bulk 14C dates taken from both units where sample MR037BC14 yields a date of 8,560 ± 30 14C yrs BP, and MR037CC14 yields a date of 13,880 ± 40 14C yrs BP (See Table 1 in Plate 2), which may correlate with Colton’s (1978) Broadway Alluvium that was deposited during the Pinedale Glaciation (12-30 ky). According to Colton (1978), Piney Creek Alluvium occupies the wetlands on the northern side of the Milton Reservoir dam. This unit has been correlated and mapped as Qa2 along the South Platte River and its major tributaries in other Colorado Geological Survey maps. In the La Salle quadrangle, unit Qa2 has two OSL age estimates which yield at 3,040 ± 260 and 3,020 ±200 SAR-OSL yrs (Palkovic and others, 2019). Two OSL age estimates in unit Qa2 were also taken at the Milliken quadrangle which yielded at 6,130 ± 470 and 3,160 ± 270 SAR OSL yrs (Palkovic and others, 2018). Deposits of unit Qa may have formed by a combination of processes. According to Smith and others (1964), during the Late Pleistocene to recent (Holocene) time, the Beebe Draw valley was covered by sediment laid down by meandering trunk streams and tributary streams as well as by sheetwash alluvium and colluvium eroded from the adjacent uplands and deposited along valley margins. This period of time encompasses the 14C ages for deposits of unit Qa unit at the MR037BC14 and MR037CC14 borrow pit sample sites. This unit is a potential source of borrow material and may be prone to expansive or collapsible soil properties, depending on silt and clay content, sediment void space, and clay mineralogy.02-03-01DMUUnit1QaQa254-246-136ESRI 24k Geology 601 Gravel 215-176-158DAS1Alluvial sedimentMediumDMU10
27QgGravel deposit of the Ancestral South Platte RiverGravel deposit of the Ancestral South Platte RiverMiddle PleistoceneGravel deposit of the Ancestral South Platte River (Middle Pleistocene) — Unit Qg consists of gravel deposited by the ancestral South Platte River within Beebe Draw. Throughout the quadrangle, this unit is overlain by fine-grained alluvium (unit Qa) and eolian deposits (unit Qes). As shown in cross section B-B’, its thickness is 1.8-16 m. The only exposure of unit Qg observed during this investigation is in the walls and floor of the borrow pit for the Steve Sharp Crane and Rigging building, near the junction of WCR 41 and WCR 24. At the pit, the unit exposure is 1.8-3 m high and has a stratigraphic sequence consisting of two sand and gravel layers with an intervening thick layer of silt and clay in between. The upper sand and gravel layer is 0.5-1.0 m thick, composed of light yellowish brown (10 YR) and light yellowish red (5Y), moderately to poorly sorted, relatively loose, fine to very coarse sand and gravel. Clasts make up 50-80% of the layer, are subrounded to rounded, and range in size from granules to 9-cm pebbles (however, pebbles are mostly “pea gravel” size, ≤ 1 cm). The clasts are composed of granitic rocks, iron-oxide concretions, yellow-brown sandstone, and quartzite (including blue-gray quartzite from Coal Creek, see Lindsey and others (2005)). Some parts of the matrix have higher amounts of silt and clay than others. A few clasts have carbonate rinds less than 1 mm thick while the matrix has no visible secondary calcium carbonate or effervescence with dilute HCl. Some of the clasts apparently are rip-up clasts of the underlying silt and clay layer and are up to 9 cm in long dimension. The middle layer is 0.2-1.0 m thick, light yellowish (10 YR) to pale brown (2.5 Y), well sorted, stratified silty clay or clayey silt, with a component of very fine to fine sand. The layer is calcareous, found having calcic nodules < 1-2 cm in diameter. Within the middle layer are thin layers of medium to coarse sand and granules about 0.5 to 5.5 cm thick. The gravel content also increases near the basal contact with the underlying sand and gravel layer. The lower sand and gravel layer’s exposure is 0.6-1.5 m thick and consists of pale brown and light brownish gray (10 YR), poorly sorted, fine to very coarse sand; gravel with clasts ranging from granules to 10-cm cobbles; and minor silt and clay. The clasts make up about 25% of the layer, are subangular to subrounded, and consist of granitic rocks, quartzite, vein quartz, iron concretions, chert, yellow and red sandstone, and volcanic rocks. The matrix does not effervesce with HCl, but some clasts have calcium carbonate rinds up to 1 mm thick. In the pit, petrified wood clasts were observed as float but from which layer it originated is not known. Previous researchers have mapped a possible equivalent to unit Qg in the Hudson quadrangle (Soister, 1965b) and the La Salle quadrangle (Colton, 1978; Palkovic and others, 2019). This equivalent has been mapped as Slocum Alluvium by its height above modern major streams (30 to 40 m, Colton, 1978) and soil development (Soister, 1965b). Hansen and Crosby (1982) did a pebble count 2-3 km south of Latham Reservoir (La Salle quadrangle) in Beebe Draw on an old terrace remnant where the rock types were 59-61% granitic rocks, 19-30% quartzite, 4-7% gneiss, and few percent sandstone, conglomerate, and porphyry. In the present investigation, four samples for OSL dating were collected in the Steve Sharp Crane and Rigging borrow pit. OSL-MRAM 2 and OSL-MRAM 2b were collected from the upper gravel layer and yield an age estimate of 115,580 ± 9,430 and 159,100 ± 13,790 SAR-OSL yrs, respectively. OSL-MRAM 1 and OSL-MRAM 1b samples were taken from the lower gravel layer, resulting in estimates of 127,730 ± 5,730 and 130,700 ± 8,530 SAR-OSL yrs, respectively. While ages are in a narrow range, it is important to note that OSL-MRAM 2b’s calculated date may be incorrect since the sample location is stratigraphically above the OSL-MRAM 1b sample location, which has the younger age. Unit Qg is a potential source for sand and gravel and for borrow material.02-03-02DMUUnit1QgQg255-255-190ESRI 24k Geology 605 Breccia 255-170-0DAS1Alluvial sediment, mostly coarse-grainedMediumDMU11
28Qg3Gravel deposit threeGravel deposit threeMiddle or Lower PleistoceneGravel deposit three (Middle or Lower Pleistocene) - Brown to light yellowish brown (10YR), poorly to very poorly sorted, very fine to very coarse sand and gravel with trace to minor silt and clay. Composition of sand is about 80% quartz, 20% feldspars and other minerals, and < 1% opaque minerals with subangular to subrounded grains. Gravel makes up 20-40% of the deposit and clasts range from granules to rare boulders up to 40 cm. According to a sieve analysis from Colton and Fitch (1974), the gravel content of this unit within the quadrangle and surrounding area can be higher, at 50-70%. During this investigation, a gravel count of 102 clasts from the borrow pit near WCR 32 and WCR37 indicates that the clast composition is about 57% granitic rocks, 25% quartzite, 9% vein quartz, 9% brown sandstone, and minor to rare red sandstone, volcanic rocks, conglomerate, and petrified wood. Typical clast shapes are subrounded to rounded and the average clast diameter is 7 cm. The lack of gneiss and schist from the pebble count observed in this unit has also been noted by Palkovic and others (2019) in the La Salle quadrangle adjacent to the north. The thickness of unit Qg3 is as great as 3 m but is generally less (Colton, 1978). The unit contains a weakly to strongly cemented Bk soil horizon, which has Stage II-III calcic carbonate development. About 40% of the clast have carbonate rinds with thicknesses of < 1 mm to 2 mm, but some rinds are as thick as 14 mm. Calcic development in the matrix ranges from no visible calcareousness but effervesces in dilute HCl acid to visible calcic-coated sand grains. Unit Qg3 is the second oldest surficial unit observed in the Milton Reservoir quadrangle. Its occurrences are scattered along the high bedrock ridge in the western portion of the quadrangle, where the gravel overlies the Denver Formation to the south and Laramie Formation to the north. Colton (1978) mapped this unit as Rocky Flats Alluvium based on elevation height above local major streams (about 75 m in the Milton Reservoir area). Previous research found the age of the Rocky Flats Alluvium ranges from ~400 ka to 2 Ma (Riihimaki and others, 2006). However, recent age dating on the Nussbaum Alluvium (possible equivalent to unit Qg4) yielded a burial age of 1.1 Ma (Odom and others, 2024). This indicates that the age of unit Qg3 is possibly younger than 1.1 Ma. Unit Qg3 is a potential source of sand and gravel and for borrow material.02-03-04DMUUnit1Qg3Qg3255-255-215ESRI 24k Geology 605 Breccia 0-92-230DAS1Alluvial sediment, mostly coarse-grainedMediumDMU12
29Qg4Gravel deposit fourGravel deposit fourLower PleistoceneGravel deposit four (Lower Pleistocene) – At Riley Mound, near the southwestern corner of the Milton Reservoir quadrangle and near northwestern corner of the Hudson quadrangle, Colton (1978) mapped the gravel alluvium unit as Rocky Flats Alluvium. However, Soister (1965b) mapped this alluvium unit as Pre-Rocky Flats Alluvium. Later publications concurred with Soister rather than with Colton (Scott, 1982; Lindsey and others, 2005). Riley Mound is about 15 m higher than surrounding gravel mounds at the southwest corner of the Milton Reservoir quadrangle and in the northwest part of the Hudson quadrangle. According to Soister (1965b), his pre-Rocky Flats Alluvium includes heavily weathered gravel with a variety of rock types including ironstone concretions. The gravel is mainly pebbles and cobbles with boulders as large as 0.5 m. Some layers are stratified sand and granules that are heavily cemented by secondary calcium carbonate. The latter can be as thick as 2.4 m. Unit Qg4 has a thickness ranging from 1.5-6.1 m. This unit may be temporally equivalent to the Nussbaum Alluvium, which is the oldest surficial deposit mapped in the Colorado Piedmont and is considered to be as old as Pliocene by previous publications (Scott, 1982; Kellogg and others, 2008). However, recent age dating of the Nussbaum Alluvium at its type location east of Pueblo, CO from Odom and others (2024) yielded a burial age date of 1.1 Ma. This indicates that the Nussbaum Alluvium is younger at this location than the Pliocene. Unit Qg4 is a potential source of sand and gravel and borrow material.02-03-05DMUUnit1Qg4Qg4234-201-144ESRI 24k Geology 605 Breccia 115-0-0DAS1Alluvial sediment, mostly coarse-grainedHighDMU13
19QuQuarternary undividedQuarternary undividedHolocene and PleistoceneQuaternary undivided (Holocene and Pleistocene) — Shown only on cross section A-A' (Plate 2). Alluvium and eolian deposits of the Ancestral South Platte River, Beebe Draw, and marginal highlands undivided. This unit may contain residuum derived from underlying weathered bedrock (Robson and others, 2000).02-03-06DMUUnit1QuQu254-246-136NoneDAS1SedimentHighDMU14
18NoneBEDROCK GEOLOGYBEDROCK GEOLOGYNoneNone03DMUHeading1BEDROCK GEOLOGYNoneNoneNoneDAS1NoneNoneDMU15
24NoneDescription of Bedrock GeologyDescription of Bedrock GeologyNoneThe Denver Formation of Paleocene and Upper Cretaceous age is the youngest bedrock unit present in the Milton Reservoir quadrangle and overlies the Laramie Formation (Dechesne and others, 2011). Bedrock in the quadrangle, however, is mostly covered by unconsolidated sediment and by heavily weathered bedrock residuum that transitions upwards into the unconsolidated sediment (Robson and others, 2000). The only location where bedrock was observed during this investigation is at the bottom of the borrow pit near the WCR 32 and WCR 37 junction. Areas mapped as bedrock in the geologic map are based on shallow depths to restrictive layer from the Natural Resources Conservation Service (NRCS) soils map of southern Weld County (Crabb, 1980). This map shows bedrock to be at shallow depths (average depth is about 80 cm). While the contact between the Denver and Laramie formations is better defined towards the west due to the Arapahoe Conglomerate lying between them, this contact is more poorly defined in the east because the conglomerate is not present. The nearest definable contact of the Denver and Laramie formations is in the southeast portion of the Platteville quadrangle; about 3 km from the Milton Reservoir quadrangle (Soister, 1965c). In addition, both the Laramie and Denver formations have lignite layers within them (Kirkham and Ladwig, 1979), making it difficult to differentiate between them in the subsurface. Dechesne and others (2011) differentiated the two units by identifying the Laramie Formation as fine grained and Denver as medium- to fine-grained, by using water well logs and borehole geophysical logs. Description of the Denver Formation in the Milton Reservoir quadrangle is taken from Soister (1965a, 1965b, 1965c), who mapped the surrounding Fort Lupton, Hudson, and Platteville quadrangles shown on the Plate 1 map plate index map (note that Soister labeled the Denver Formation as Dawson Formation, Kdw). The Laramie Formation description is from the Platteville quadrangle map (Soister, 1965c).03-01DMUUnit1Description of Bedrock GeologyNoneNoneNoneDAS1NoneNoneDMU16
7PeKdDenver FormationDenver Formationlower Paleogene to upper CretaceousDenver Formation (Lower Paleogene to Upper Cretaceous) — Dark-gray shale and clay with some siltstone, yellowish-gray arkosic sandstone, and partly calcareous sandstone. Calcareous ironstone concretions of 1.2-1.8 m diameter occur in the lower shaly part of the unit and are smaller in the upper sandy part; some of the concentrations contain abundant fossil leaf fragments. The unit has rare lenticular coal beds less than 0.9 m thick. Some sandstone and ironstone concretions have a grain size range from coarse sand to small pebbles. Sandstone beds are commonly lenticular and commonly have numerous cut and fill structures with some intraformational conglomerate. Thickness ranges from 183 m to less than 61 m. In the Milton Reservoir quadrangle, cross section A-A’ shows that the Denver Formation is less than 10 m, based on 1-m pixel digital elevation model imagery and the Laramie Formation structure contour map of Dechesne and others (2011).03-01-01DMUUnit1:KdPeKd205-137-102NoneDAS1Sandstone and mudstoneLowDMU17
8KlLaramie FormationLaramie Formationupper CretaceousLaramie Formation (Upper Cretaceous) — Shale, calcareous fine- to medium-grained sandstone, siltstone, clay, carbonaceous shale, and evenly stratified coal beds about 1 m thick. Ironstone nodules are found throughout the unit. From 76-152 m above the base, as many as six subbituminous coal beds occur; individual beds are 0.6-1.8 m thick. Historic coal mines are present in the map area where mine workings advanced through the thin overlying surficial deposits. Massive beds of sandstone and shale occur within the lower 58 m of the unit. The uppermost of these is the “B” sandstone which is about 12-18 m thick. The lowest part of the Laramie Formation along with the underlying Fox Hills Sandstone makes the Fox Hills-Laramie aquifer, which serves as a principal bedrock aquifer of the Denver Basin. In the present investigation, the only location where the Laramie Formation was observed is at the bottom of the borrow pit near the WCR 32 and WCR 37 junction. The bedrock was originally overlain by unit Qg3 which was removed during pit operation. The unit is a greenish-gray (Gley 1) silty clay or clayey silt with about 20% fine sand. Calcic carbonate nodules range from less than 1 to 2 mm and there are bands of iron oxide, mostly about 3 mm thick but locally as thick as 14 mm. Although not seen in situ in unit Kl, ironstone concretions fragments are commonly found in the unit Qg3 gravel that overlies this unit. Cross section A-A’ shows Laramie Formation thickness as 31-113 m. The variation in thickness is due to the unconformity between the Laramie and overlying Denver Formation (Dechesne and others, 2011; Raynolds, 2022).03-01-02DMUUnit1KlKl168-230-138NoneDAS1Sandstone and mudstoneMediumDMU18
9KfhFox Hills SandstoneFox Hills Sandstoneupper CretaceousFox Hills Sandstone (Upper Cretaceous) — Shown in cross section only. Greenish-buff to light-yellow, white fine to coarse grained quartzose sandstone. Lower part is cross-bedded and upper is massive. Contains some thin beds of olive-gray sandy shale and gray to brown hard calcareous concretions. Approximately 89 to 99 m thick.03-01-03DMUUnit1KfhKfh235-255-204NoneDAS1SandstoneMediumDMU19
10KpPierre ShalePierre Shaleupper CretaceousPierre Shale (Upper Cretaceous) — Shown in cross section only. Primarily composed of dark gray marine fossiliferous shale and siltstone interbedded with sandstone. Bentonite beds are common in the lower part. Calcareous concretions are common throughout the unit. Approximately 1,894 to 2,037 m thick.03-01-04DMUUnit1KpKp137-137-68NoneDAS1MudstoneHighDMU20
11KnNiobrara FormationNiobrara Formationupper CretaceousNiobrara Formation (Upper Cretaceous) — Shown in cross section only. Very fissile dark-gray, marine, fossiliferous shale with thin layers of micritic limestone. Unit is an important oil and gas source in the Denver Basin. Approximately 70 to 105 m thick.03-01-05DMUUnit1KnKn235-255-178NoneDAS1MudstoneHighDMU21
12KcggColorado GroupColorado Groupupper CretaceousColorado Group (Upper Cretaceous) — Shown in cross section only. Unit includes Carlile Shale (near-shore sandstone and shale), Graneros Shale (shale with interbedded sandstone), and Greenhorn Limestone (limestone, shale, and chalky shale). Combined thickness is approximately 132 to 173 m.03-01-06DMUUnit1KcggKcgg204-255-48NoneDAS1Mostly mudstoneHighDMU22
13KdDakota GroupDakota Grouplower CretaceousDakota Group (Lower Cretaceous) — Shown in cross section only. Unit includes the South Platte Formation (sandstone and shale) and Lytle Formation (conglomeratic sandstone and mudstone). No wells on Cross Section A penetrated through the Dakota, however, the combined thickness in Cross Section A is about 20 to 86 m. Around the Milliken area, the Dakota Group has been reported to be 81 m in total thickness (Colton, 1978).03-01-07DMUUnit1KdKd204-204-102NoneDAS1Clastic sedimentary rockMediumDMU23
26BedrockBedrock undividedBedrock undividedPaleogene to upper CretaceousNone03-01-08DMUUnit1PeKd / KlNone205-137-102NoneDAS1Sandstone and mudstoneMediumDMU24
25waterwaterwaterHoloceneNone04DMUHeading1Nonewater199-234-250NoneDAS1Water or iceHighDMU25

Glossary

OBJECTIDTermDefinitionDefinitionSourceIDGlossary_ID
18borderMargin or outline of a map.GeMS1GLO01
19BoreholeA circular hole made by drilling technique, such as an oil or water well.GEODICT1GLO02
32Borrow PitAn excavated area where borrow has been obtained.GEODICT1GLO03
35BPBefore present (with "present" fixed as the year 1950).GEODICT1GLO04
24C14Carbon-14 (C14) is a heavy radioactive isotope useful in dating geologic material.GEODICT1GLO05
1certainIdentity 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-013-2006GLO06
31CMU LinesFeatures created to add clarity to the CMU includeing deposits groups and agesDAS1GLO07
21Coal MineExcavation for the extration of coal resources.GEODICT1GLO08
3contactA geological contact is a boundary which separates one rock body from another. A contact can be formed during deposition, by the intrusion of magma, or through faulting or other deformation of rock beds that brings distinct rock bodies into contact.GEODICT1GLO09
17cross sectionA diagram representing the geologic features intersecting a vertical plane, used to illustrate structure and stratigraphy that would otherwise be hidden underground.GEODICT1GLO10
5DMUHeading1GeMS hierarchy formatting termGeMS1GLO11
7DMUHeading2GeMS hierarchy formatting termGeMS1GLO12
6DMUUnit1GeMS hierarchy formatting termGeMS1GLO13
4dune crestRidge of wind-blown dune.GEODICT1GLO14
30elev tickA hatch mark shown on the edges of geologic cross sections to denote the elevationDAS1GLO15
15eolian blowoutDepression in sand dune ecosystem caused by the removal of sediments by wind.GEODICT1GLO16
22GeotechnicalDrill hole for acquisition of geotechnic data.GEODICT1GLO17
29HighUnusual or considerable in degree, power, intensity, etc.DICT1GLO18
25inferred contactA Contact derived from the basis of the conclusion of facts or premises from geological evidence and assumptions.GEODICT1GLO19
28LowOf inferior character or qualityDICT1GLO20
27MediumSomething intermediate in nature or degreeDICT1GLO21
23OSLOptically Stimulated Luminescence (OSL) is a method for measuring doses from ionizing radiation for dating of mainly geologic sediments.GEODICT1GLO22
26paleo boundaryAncient prehistoric contact.GEODICT1GLO23
16PaleovalleyA prehistoric valley.GEODICT1GLO24
2questionableIdentity 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-013-2006GLO25
20Water WellA well that extracts water from the saturated zone or that shich yields useful supplies of water.GEODICT1GLO26
33wireframeDiagram of something in which only lines are shown,DICT1GLO27
34yearThe time taken by the earth to make one revolution around the sun.DICT1GLO28

MiscellaneousMapInformation

OBJECTIDMapPropertyMapPropertyValueMiscellaneousMapInformation_ID
2Mineral ResourcesThe Milton Reservoir quadrangle is located in the western part of the Denver Basin and the southern part of Weld County. The quadrangle contains oil and gas, coal, and sand and gravel mineral resources. The quadrangle lies within the center of the Wattenberg oil and gas field, which covers most of Weld County and is one of the most productive and active fields in Colorado. The principal production horizon in the Wattenberg field is the Niobrara Formation, but other horizons include the middle member of the Pierre Shale (Hygiene “Shannon” Sandstone Member), the Codell Sandstone Member of the Niobrara Formation, and the Dakota Group (Muddy (“J”) Sandstone and “D” Sandstone) (Fisherman, 2005). In 2022, Weld County was ranked first for oil and natural gas (including coalbed gas) production in Colorado (COGCC, 2022). The Denver Basin contains two units with coal deposits: the Upper Cretaceous Laramie Formation and the Paleocene and Upper Cretaceous Denver Formation. Coal quality in the Laramie Formation ranges from lignite to subbituminous while the Denver Formation coals are lignite (CGS, 2002). About 30 km southwest of the Milton Reservoir quadrangle is the Boulder-Weld coal field which was productive from 1863 to 1979. All the coal there was mined from the Laramie Formation (CGS, 2002). There are three historic coal mines shown on the Plate 1 geologic map that are in the northern part of the quadrangle. One named “Platteville A" is by the western boundary in section 14 of the USGS 1951 Milton Reservoir topographic map and has been mapped by the Colorado Geological Survey (Carroll, 2006). This mine was in operation from 1939 to 1940 and produced 202 tons of coal (Turney and Murray-Williams, 1983). The second mine labeled “Platteville (Old)” location is not known for certain but is near the intersection of WCR 39 and WCR 32 (sections 17, 18, 19, and 20 on the USGS 1951 Milton Reservoir topographic map). A third mine southeast of Milton Reservoir named the “3 Link Coal Mine” is in section 14 on the 1951 USGS topographic map. This mine is only shown on the 1902 USGS 1:125,000 topographic map of the area that includes Greeley and Fort Lupton. Field verification was limited due to access restrictions from landowners and precise mine locations could not be determined from aerial photography or lidar imagery. Surface subsidence caused by coal mining in the Laramie Formation is a well-documented geological hazard, especially within the Boulder-Weld coal field (Amuedo and Ivey, 1975; CGS, 2001). The Laramie and Denver Formation coals are a potential source of coalbed methane in the Denver Basin (Wray and Koenig, 2001). However, factors such as water quality and rights, groundwater resource protection, economics, and the decline of coalbed methane due to the increase of unconventional natural gas production (horizon drilling and hydraulic fracturing) presently work against making this resource economically feasible (Wray and Koenig, 2001; O’Keeffe and Berry, 2021). Units Qg1, Qg2, and Qg3 are potential sources of sand and gravel. However, there are no active or historic gravel quarries in these units within the Milton Reservoir quadrangle. Unit Qg1 has a thick overburden of valley fill sediment (unit Qa), making it not economically feasible (Schwochow and others, 1974). Also, units Qg2 and Qg3 are extensively weathered, contain large amounts of pedogenic calcium carbonate, and are of limited areal extent. Units Qg1, Qg2, and Qg3 can be used as a local source for borrow material. The borrow pit by the WCR 32 and WCR 37 junction used unit Qg2 sediment for the construction of WCR 32. Steve Sharp Crane and Rigging’s borrow pit sourced unit Qg1 and overlaying unit Qa for aggregate to make cement for its facility. The Laramie-Fox Hill aquifer includes two relatively thick sandstone units at the basal portion of the Laramie Formation, as well as the underlying Fox Hill Sandstone. The aquifer occurs throughout the Denver Basin, including the Milton Reservoir quadrangle. Its thickness is as much as 107 m, but water is pumped from zones that rarely are thicker than ~60 m. The aquifer underlies the surficial deposits throughout the quadrangle and is generally under artesian conditions (Toppler and others, 2003). According to the Colorado Division of Water Resources (CO DWR, 2022), well depths for the Laramie-Fox Hill aquifer are commonly about 91 m in the quadrangle. Another bedrock aquifer in the southern part of the quadrangle is the Denver aquifer (also called the Arapahoe aquifer in some well records), but only four of 445 water wells in the quadrangle use this aquifer (CO DWR, 2022). Surficial units such as the gravel deposits from the ancestral South Platte River (unit Qg1) and eolian deposits (unit Qes) can be local sources for groundwater. The maximum water well depth in the quadrangle is 256 m and wells have an average production yield of 15 gallons per minute (gpm) (CO DWR, 2022). The upper valley fill deposits of Beebe Draw (Unit Qa) locally may contain swelling clays that can impact building foundations and infrastructure construction. Near the quadrangle eastern boundary on WCR 30, a subsoil investigation for a single home built on unit Qa determined that clay at a depth about 2 m (6 feet) has a swelling expansion potential of 0.4% and at 7.8% at 3.4 m (High Plains Engineering, 2005). In the upland area, shale bedrock and weathered bedrock clay such as that of the Laramie Formation could also be a potential source of swelling clays (Church and Association. Inc., 2001). Units Qe and Qes with locally abundant clay and silt, could also be a source of hydrocompactive (or collapsible) soils. When such types of soils are dry, the finer-sized particles (silt and clay) act as binding agents to soil grains and increase the compressive strength of the soil. When the soils are wet or saturated, the binding agents have much less cohesive strength and expansive clay minerals can expand and (or) grains can re-orient and pack into a denser configuration such that void space in the soil is reduced and collapse may occur. This compaction can cause settlement at and near the ground surface with possible resultant damage to load-bearing structures (White and Greenman, 2008). The sandier deposits of unit Qes may be subject to erosion (Empire Laboratories. Inc., 1985). The Federal Emergency Management Agency (FEMA) does not have any designated flood boundaries delineated within the Milton Reservoir quadrangle (see FEMA at https://msc.fema.gov/ for more information about flood hazard designation and hazard zone maps). However, 100-year floodplains have been mapped along the western and northwestern edge of Milton Reservoir and Platte Valley Canal (Arix. Inc., 1984). Seismic risk within and near the Milton Reservoir quadrangle appears to be low. Using the U.S. Geological Survey Online Earthquake Catalogue (https://earthquake.usgs.gov/earthquakes/search/), from 1960 to 2023, there has been no earthquakes greater than 1 magnitude on the Richter scale.MMI01
4Geologic HistoryThe Milton Reservoir quadrangle is situated about 70 km northeast of Denver, Colorado and within the Front Range Urban Corridor. The quadrangle lies within the northern part of the Colorado Piedmont, a physiographic province surrounded by the High Plains to the north and east and the Rocky Mountains to the west (Fenneman, 1931; Leonard, 2002; Smith and others, 2016). The Colorado Piedmont largely lacks rocks and sediment of Paleogene and Neogene age, because of fluvial erosion and geomorphic evolution in the South Platte River and Arkansas River drainage basins during the middle Pliocene (Madole, 1991). The result from these processes is a region dominated by erosion that is topographically lower than the surrounding physiographic provinces. The elevation range within the quadrangle is from 4,723-5,195 ft (1440-1583 m) above mean sea level. The low relief of the landscape is due to continued incision by the modern South Platte River and its tributaries to the west, Box Elder Creek to the east, and the ancestral South Platte River (Beebe Draw) in the center of the quadrangle. The South Platte River and its tributaries mostly flow to the northwest and northeast, Box Elder Creek flows to the north and northeast, and the gradient of Beebe Draw trends down to the north. Surficial deposits cover the bedrock throughout the quadrangle, and there are no natural bedrock exposures, although small areas of bedrock are mapped within the Milton Reservoir quadrangle. As shown in the geologic map (Plate 1), the contact between the Upper Cretaceous Laramie Formation (on the north and east) and the Upper Cretaceous-Paleocene Denver Formation (on the south and west) is buried beneath surficial deposits; the approximate contact shown on the map is from Dechesne and others (2011). The Denver Formation is a dark gray shale with arkosic sandstone and locally calcareous sandstone. The Laramie Formation is chiefly shale and minor amounts of fine to medium-grained sandstone, and siltstone (Soister 1965a, 1965b, 1965c). The Milton Reservoir quadrangle lies midway along the western edge of the Denver Basin (Dechesne and others, 2011). The Denver Basin is a symmetrical, oval-shaped, structural basin that extends from north of Pueblo to Greeley and from the Front Range into southwest Nebraska and southeast Wyoming. The formation of the Denver Basin began about 300 million years ago during the uplift of the Ancestral Rocky Mountains. During the Late Cretaceous (100-66 million years ago), the Western Interior Seaway (WIS) covered an extensive area that includes the area of the present day Denver Basin and deposited a thick package of Upper Cretaceous marine shale and carbonate sediments. On the western margins of the seaway, the Laramie Formation was deposited on low coastal plains. About 70 million years ago, the modern Rocky Mountains began to uplift during the Laramide Orogeny. At the same time, the WIS was retreating to the east and south. Sediment eroded from uplifted Precambrian, Paleozoic, and Mesozoic rocks exposed in the mountains of the Front Range was transported eastward by Paleogene paleofluvial drainage systems and were deposited in the Denver Basin, forming what is now known as the Denver Formation. Thereafter, other Paleogene and Neogene units were also deposited. By the early-middle Pliocene time this pattern changed from aggradation to incision due to an increase in precipitation, and tectonic uplifts in the Rocky Mountains (Duller, and others, 2012; Marder and others, 2023) that continued during the Quaternary. One of the results of this pattern change was the extensive removal of the Paleogene and Neogene rocks in the Colorado Piedmont, leaving mostly Paleocene and Cretaceous rocks exposed. Since the beginning of the Pleistocene, the Colorado Piedmont region has undergone cyclic geomorphic responses to climate variations related to multiple glaciation periods. The results from the cyclic patterns are alternate stages of erosional scouring and of deposition of coarse-grained sediments (examples are in Bryan and Ray, 1940; Hunt, 1954; Scott, 1963; Lindsey and others, 2005). Unit Qg2 and Qg3 are coarse-grained, fluvial gravel units that were deposited by high energy streams flowing eastward from the mountains, most likely during interglacial periods during the early and middle Pleistocene although unit Qg3 may have been part of a broad thick alluvial fan deposit that extended from the Front Range to the northeast near Sterling (Scott, 1982). Colton and Fitch (1974) mapped these gravel units at Riley Mound and just north of the Milton Reservoir-La Salle quadrangle boundary. Colton (1978) mapped the general area again that included the area of Riley Mound. During the field work for the present map, unit Qg2 was also observed at a borrow pit near the WCR 32 and WCR 37 junction and about 4 km north by the Milton Reservoir-La Salle quadrangle boundary; the material has been extensively weathered and mixed with eolian sediments and altered by pedogenic processes. Gravel was also observed at Riley Mound during this investigation, but it has been obscured by recent grading activities. Based on elevation above modern streams, Colton (1978) mapped the gravel unit at Riley Mound and at the WCR 32 and WCR 37 junction borrow pit as Rocky Flats Alluvium (100 m above modern streams). Previously, Rocky Flats Alluvium (unit Qg2) has an estimated age of ~400 ka to 2 Ma from (Riihimaki and others, 2006). In contrast, Soister (1965b) mapped Riley’s Mound at Pre-Rocky Flats Alluvium (unit Qg3) which may be as old as the Pliocene (Scott, 1982). However, recent age dating on the Nussbaum Alluvium (possible correlation with unit Qg3) shows that its burial age is about 1.1 Ma (Odom and others, 2024), indicating that unit Qg3 is possibly younger than the Pliocene and unit Qg2 is younger than 1.1 Ma. Due to the gravelly and coarse-grained nature of unit Qg2 and Qg3, they have a higher resistance to erosion than the surrounding finer-grained sediment and relatively soft bedrock. Later erosion of the surrounding sediments and bedrock left this gravel units as isolated remnants along low hilltops such as the ridgeline on the western side of the Milton Reservoir quadrangle. According to Lindsey and others (2005), in about Early Pleistocene time the South Platte River generally followed its present course. Then in about the middle Pleistocene time, the river shifted to the east and flowed in what is now called Beebe Draw. To the southeast of the quadrangle boundary, the ancestral Box Elder Creek was a tributary to the South Platte River. During its flow through Beebe Draw, fluvial gravel was deposited on the valley floor (unit Qg1). Later, the South Platte River shifted westward, back to its modern course, during the late Pleistocene (Lindsey and others, 2005). The cause of this shift may have been stream piracy by a tributary stream of the ancestral Cache La Poudre River (Smith and others, 1964) or possibly due in part to neotectonics (Shawe and others, 2008). After the piracy of the ancestral South Platte River, the ancestral Box Elder Creek continued to flow through Beebe Draw until it also was pirated to its present course by a tributary to the north of Hudson. After the abandonment, small meandering tributary trunk streams deposited sediment that covered the floor of Beebe Draw containing unit Qg1 and burying it with relatively fine-grained alluvium during the late Pleistocene and Holocene (Smith and others, 1964). In addition, sheetwash and mass-wasting processes on the surrounding valley sides may also have also contributed sediment into Beebe Draw. In this map, the younger alluvium is designated as unit Qa. The Beebe Draw paleovalley has been previously mapped and developed for water wells (Smith and others, 1964; Hillier and Schneider, 1979; Robson, 1996; Robson and others, 2000). In the La Salle quadrangle to the north, Colton (1978) designated the Beebe Draw gravel as Slocum Alluvium based on its stream level elevation (30-40 m above modern streams). In field work for the present map, an excellent exposure of the valley-fill sequence was observed at the Steve Sharp Crane and Rigging borrow pit and samples were collected for age determinations (See Plate 1 Description of Map Units and Tables 1 and 2). Eolian deposits (units Qes and Qe) cover about 84% of the quadrangle. Locally, these units broadly cover much of the Colorado Piedmont and eastern plains. The main source of the windblown sand is alluvium of the South Platte River and its tributaries, with a minor source being derived from surrounding bedrock. Predominantly northwest winds transported sediments from the South Platte River valley floor and deposited eolian sand and silt throughout the quadrangle. Locally, deposits of units Qe and Qes may have a much higher fines content (silt and clay) owing, perhaps, to the erosion of the underlying or nearby bedrock and alluvial units (rich in silt and clay) by eolian intermixing. Compared to the southern part of the quadrangle, the eolian deposits of the Milton Reservoir quadrangle are sandier in the northern part, especially around the Beebe Draw Farms subdivision. Units Qe and Qes in and near the Milton Reservoir area are of Holocene age, but are known to be as old as late Pleistocene in other places in the Colorado Piedmont (Madole and others, 2005). Late Pleistocene dunes are more extensive than those of late Holocene age due to major eolian deposition by dominantly northwest winds during the Pinedale Glaciation (Madole and others, 2005; Madole, 2016).MMI02
5AcknowledgmentsThe author would like to thank the following for their assistance on this investigation. Michael O’Keefe (CGS) assisted the author in the field, research, provided valuable suggestions, discussions, and guidance. Stephen Keller (CGS) was a peer reviewer, assisted in the field, and provided the author constructive information. Ralph Shroba (Emeritus USGS and CGS) was a peer reviewer and provided valuable suggestions to improve this map. Scott Fitzgerald (CGS) assembled the lidar imagery of the quadrangle and surrounding areas. Jill Carson (CGS) assisted with obtaining geotechnical investigation documents from the Colorado State Archive. Steven L. Forman of Baylor University, Waco, Texas performed the optically stimulated luminescence (OSL) analyses and Beta Analytics, Inc., Miami, Florida performed the radiocarbons analyses. Jonathan White (CGS STATEMAP Program Manager) and Matthew Morgan (State Geologist and CGS Director) reviewed the final product. Caitlin Bernier and David “Barney” Barnett of Pangea Geospatial, Gunnison, Colorado produced the final map plates and GIS files. Steve Sharp from Steve Sharp Crane and Rigging Inc. allowed the author to visit and sample their borrow pit in Beebe Draw. Jeff DeLisio and the Farmers Reservoir & Irrigation Company permitted the author access to areas around Milton Reservoir. The author would also like to thank Bob Warner, Roy Wardell, Juan Loya, Dianne and Chester Norgren, and other landowners in and around the Milton Reservoir quadrangle who permitted the author to visit and work on their properties.MMI03
6RefrencesAmuedo and Ivey, 1975, Coal mine subsidence and land use in the Boulder-Weld coalfield, Boulder and Weld Counties, Colorado: Colorado Geological Survey Environmental Geology 9 [available at https://coloradogeologicalsurvey.org/publications/coal-mine-subsidence-land-use-boulder-weld-colorado/].MMI04
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58RefrencesPrescott, J.R., and Hutton, J.T., 1994, Cosmic ray contributions to dose rates for luminescence and ESR dating: Large depth sand long-term time variations: Radiation Measurements, v. 23, p. 497- 500.MMI53
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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, 5 rows
DescriptionOfMapUnits, nonspatial table, 25 rows
GeoMaterialDict, nonspatial table, 101 rows
Glossary, nonspatial table, 28 rows
MiscellaneousMapInformation, nonspatial table, 76 rows
GeologicMap, feature dataset
GeologicLines, simple polyline feature class, 19 rows
GenericPoints, simple point feature class, 57 rows
CartographicLines, simple polyline feature class, 2 rows
OverlayPolys, simple polygon feature class, 241 rows
GeochronPointsAnno, annotation polygon feature class, 9 rows
MapUnitPolysAnno, annotation polygon feature class, 53 rows
GeochronPoints, simple point feature class, 12 rows
ContactsAndFaults, simple polyline feature class, 183 rows
MapUnitPolys, simple polygon feature class, 82 rows
GenericPointsAnno, annotation polygon feature class, 57 rows
GeologicMap_topology, topology
CorrelationOfMapUnits, feature dataset
CMUMapUnitPolys, simple polygon feature class, 14 rows
CMULines, simple polyline feature class, 35 rows
CMULinesAnno, annotation polygon feature class, 16 rows
CMUMapUnitPolysAnno, annotation polygon feature class, 14 rows
CrossSectionA, feature dataset
CSAMapUnitPolys, simple polygon feature class, 7 rows
CSAContactsAndFaults, simple polyline feature class, 20 rows
CSA_CartoLines, simple polyline feature class, 17 rows
CSA_CartoLinesAnno, annotation polygon feature class, 22 rows
CSA_DHCollar, simple point feature class, 31 rows
CSA_DHTrace, simple polyline feature class, 31 rows
CSA_DHCollarAnno, annotation polygon feature class, 31 rows
CSAMapUnitPolysAnno, annotation polygon feature class, 7 rows
CrossSectionB, feature dataset
CSBContactsAndFaults, simple polyline feature class, 15 rows
CSBMapUnitPolys, simple polygon feature class, 6 rows
CSB_DHTrace, simple polyline feature class, 21 rows
CSB_CartoLines, simple polyline feature class, 22 rows
CSB_CartoLinesAnno, annotation polygon feature class, 24 rows
CSB_DHCollar, simple point feature class, 21 rows
CSB_DHCollarAnno, annotation polygon feature class, 21 rows
CSBMapUnitPolysAnno, annotation polygon feature class, 6 rows