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This file should be accompanied by OF-23-04_Milton_Reservoir.gdb-ValidationErrors.html and a metadata summary from mp
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.
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
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
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.
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
OBJECTID
Source
Notes
URL
DataSources_ID
2
This study
None
None
DAS1
9
Online dictionary
None
https://dictionary.com/
DICT1
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
6
GeMS standard
None
https://ngmdb.usgs.gov/Info/standards/GeMS/
GeMS1
8
Klaus 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.
None
https://www.americangeosciences.org/pubs/glossary
GEODICT1
DescriptionOfMapUnits
OBJECTID
MapUnit
Name
FullName
Age
Description
HierarchyKey
ParagraphStyle
Label
Symbol
AreaFillRGB
AreaFillPatternDescription
DescriptionSourceID
GeoMaterial
GeoMaterialConfidence
DescriptionOfMapUnits_ID
21
None
DESCRIPTION OF MAP UNITS
DESCRIPTION OF MAP UNITS
None
None
01
DMUHeading1
DESCRIPTION OF MAP UNITS
None
None
None
DAS1
None
None
DMU01
23
None
DMU description
DMU description
None
A 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).
01-01
DMUUnit1
DMU description
None
None
None
DAS1
None
None
DMU02
14
None
SURFICIAL DEPOSITS
SURFICIAL DEPOSITS
None
None
02
DMUHeading1
SURFICIAL DEPOSITS
None
None
None
DAS1
None
None
DMU03
15
None
HUMAN-MADE DEPOSITS
HUMAN-MADE DEPOSITS
None
None
02-01
DMUHeading2
HUMAN-MADE DEPOSITS
None
None
None
DAS1
None
None
DMU04
1
af
Artificial Fill
Artificial Fill
uppermost Holocene
Artificial 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.
02-01-01
DMUUnit1
af
af
255-255-255
None
DAS1
"Made" or human-engineered land
High
DMU05
16
None
EOLIAN DEPOSITS
EOLIAN DEPOSITS
None
None
02-02
DMUHeading2
EOLIAN DEPOSITS
None
None
None
DAS1
None
None
DMU06
22
Qes
Eolian sand
Eolian sand
Holocene
Eolian 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.
02-02-01
DMUUnit1
Qes
None
255-247-153
None
DAS1
Dune sand
High
DMU07
6
Qe
Eolian sediment
Eolian sediment
Holocene and upper Pleistocene
Eolian 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.
02-02-02
DMUUnit1
Qe
Qe
255-252-223
None
DAS1
Eolian sediment
Medium
DMU08
17
None
ALLUVIAL DEPOSITS
ALLUVIAL DEPOSITS
None
None
02-03
DMUHeading2
ALLUVIAL DEPOSITS
None
None
None
DAS1
None
None
DMU09
2
Qa
Alluvium
Alluvium
Holocene and upper Pleistocene
Alluvium, 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.
02-03-01
DMUUnit1
Qa
Qa
254-246-136
ESRI 24k Geology 601 Gravel 215-176-158
DAS1
Alluvial sediment
Medium
DMU10
27
Qg
Gravel deposit of the Ancestral South Platte River
Gravel deposit of the Ancestral South Platte River
Middle Pleistocene
Gravel 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.
02-03-02
DMUUnit1
Qg
Qg
255-255-190
ESRI 24k Geology 605 Breccia 255-170-0
DAS1
Alluvial sediment, mostly coarse-grained
Medium
DMU11
28
Qg3
Gravel deposit three
Gravel deposit three
Middle or Lower Pleistocene
Gravel 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.
02-03-04
DMUUnit1
Qg3
Qg3
255-255-215
ESRI 24k Geology 605 Breccia 0-92-230
DAS1
Alluvial sediment, mostly coarse-grained
Medium
DMU12
29
Qg4
Gravel deposit four
Gravel deposit four
Lower Pleistocene
Gravel 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.
02-03-05
DMUUnit1
Qg4
Qg4
234-201-144
ESRI 24k Geology 605 Breccia 115-0-0
DAS1
Alluvial sediment, mostly coarse-grained
High
DMU13
19
Qu
Quarternary undivided
Quarternary undivided
Holocene and Pleistocene
Quaternary 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).
02-03-06
DMUUnit1
Qu
Qu
254-246-136
None
DAS1
Sediment
High
DMU14
18
None
BEDROCK GEOLOGY
BEDROCK GEOLOGY
None
None
03
DMUHeading1
BEDROCK GEOLOGY
None
None
None
DAS1
None
None
DMU15
24
None
Description of Bedrock Geology
Description of Bedrock Geology
None
The 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).
03-01
DMUUnit1
Description of Bedrock Geology
None
None
None
DAS1
None
None
DMU16
7
PeKd
Denver Formation
Denver Formation
lower Paleogene to upper Cretaceous
Denver 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).
03-01-01
DMUUnit1
:Kd
PeKd
205-137-102
None
DAS1
Sandstone and mudstone
Low
DMU17
8
Kl
Laramie Formation
Laramie Formation
upper Cretaceous
Laramie 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).
03-01-02
DMUUnit1
Kl
Kl
168-230-138
None
DAS1
Sandstone and mudstone
Medium
DMU18
9
Kfh
Fox Hills Sandstone
Fox Hills Sandstone
upper Cretaceous
Fox 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.
03-01-03
DMUUnit1
Kfh
Kfh
235-255-204
None
DAS1
Sandstone
Medium
DMU19
10
Kp
Pierre Shale
Pierre Shale
upper Cretaceous
Pierre 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.
03-01-04
DMUUnit1
Kp
Kp
137-137-68
None
DAS1
Mudstone
High
DMU20
11
Kn
Niobrara Formation
Niobrara Formation
upper Cretaceous
Niobrara 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.
03-01-05
DMUUnit1
Kn
Kn
235-255-178
None
DAS1
Mudstone
High
DMU21
12
Kcgg
Colorado Group
Colorado Group
upper Cretaceous
Colorado 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.
03-01-06
DMUUnit1
Kcgg
Kcgg
204-255-48
None
DAS1
Mostly mudstone
High
DMU22
13
Kd
Dakota Group
Dakota Group
lower Cretaceous
Dakota 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).
03-01-07
DMUUnit1
Kd
Kd
204-204-102
None
DAS1
Clastic sedimentary rock
Medium
DMU23
26
Bedrock
Bedrock undivided
Bedrock undivided
Paleogene to upper Cretaceous
None
03-01-08
DMUUnit1
PeKd / Kl
None
205-137-102
None
DAS1
Sandstone and mudstone
Medium
DMU24
25
water
water
water
Holocene
None
04
DMUHeading1
None
water
199-234-250
None
DAS1
Water or ice
High
DMU25
Glossary
OBJECTID
Term
Definition
DefinitionSourceID
Glossary_ID
18
border
Margin or outline of a map.
GeMS1
GLO01
19
Borehole
A circular hole made by drilling technique, such as an oil or water well.
GEODICT1
GLO02
32
Borrow Pit
An excavated area where borrow has been obtained.
GEODICT1
GLO03
35
BP
Before present (with "present" fixed as the year 1950).
GEODICT1
GLO04
24
C14
Carbon-14 (C14) is a heavy radioactive isotope useful in dating geologic material.
GEODICT1
GLO05
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
GLO06
31
CMU Lines
Features created to add clarity to the CMU includeing deposits groups and ages
DAS1
GLO07
21
Coal Mine
Excavation for the extration of coal resources.
GEODICT1
GLO08
3
contact
A 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.
GEODICT1
GLO09
17
cross section
A diagram representing the geologic features intersecting a vertical plane, used to illustrate structure and stratigraphy that would otherwise be hidden underground.
GEODICT1
GLO10
5
DMUHeading1
GeMS hierarchy formatting term
GeMS1
GLO11
7
DMUHeading2
GeMS hierarchy formatting term
GeMS1
GLO12
6
DMUUnit1
GeMS hierarchy formatting term
GeMS1
GLO13
4
dune crest
Ridge of wind-blown dune.
GEODICT1
GLO14
30
elev tick
A hatch mark shown on the edges of geologic cross sections to denote the elevation
DAS1
GLO15
15
eolian blowout
Depression in sand dune ecosystem caused by the removal of sediments by wind.
GEODICT1
GLO16
22
Geotechnical
Drill hole for acquisition of geotechnic data.
GEODICT1
GLO17
29
High
Unusual or considerable in degree, power, intensity, etc.
DICT1
GLO18
25
inferred contact
A Contact derived from the basis of the conclusion of facts or premises from geological evidence and assumptions.
GEODICT1
GLO19
28
Low
Of inferior character or quality
DICT1
GLO20
27
Medium
Something intermediate in nature or degree
DICT1
GLO21
23
OSL
Optically Stimulated Luminescence (OSL) is a method for measuring doses from ionizing radiation for dating of mainly geologic sediments.
GEODICT1
GLO22
26
paleo boundary
Ancient prehistoric contact.
GEODICT1
GLO23
16
Paleovalley
A prehistoric valley.
GEODICT1
GLO24
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
GLO25
20
Water Well
A well that extracts water from the saturated zone or that shich yields useful supplies of water.
GEODICT1
GLO26
33
wireframe
Diagram of something in which only lines are shown,
DICT1
GLO27
34
year
The time taken by the earth to make one revolution around the sun.
DICT1
GLO28
MiscellaneousMapInformation
OBJECTID
MapProperty
MapPropertyValue
MiscellaneousMapInformation_ID
2
Mineral Resources
The 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
4
Geologic History
The 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
5
Acknowledgments
The 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
6
Refrences
Amuedo 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
7
Refrences
Arix, Inc., 1984, Beebe Draw Farms, Arix project no. 83255.00: Colorado State Archives, Document ID WE-84-0013.
MMI05
8
Refrences
Bryan, K., and Ray, L.L., 1940, Geologic antiquity of Lindenmeier site in Colorado: Smithsonian Misc. Colln., v. 99, p. 65-86.
MMI06
9
Refrences
Carroll, C.J., 2006, Coal fields and resources of Colorado: Colorado Geological Survey Map Series 43 [Available at https://coloradogeologicalsurvey.org/publications/coal-resource-maps-colorado/].
MMI07
10
Refrences
Church and Associates, Inc., 2001, Engineering geology report for replat lot 13, Weisner subdivision - first filing, part of the S ½ of section 7, township 2 north, range 65 west of the 6th p.m. Weld County, Colorado: Colorado State Archives, Document ID WE-02-0014.
MMI08
11
Refrences
Colorado Division of Water Resources (CO DWR), 2022, Driller’s logs incorporated with water-well permits [Available at https://dwr.colorado.gov/services/data-information/gis/].
MMI09
12
Refrences
Colorado Geological Survey (CGS), 2001, RockTalk v. 4, no. 4, October 2001- Ground subsidence and settlement hazards [Available at https://coloradogeologicalsurvey.org/publications/rocktalk-ground-subsidence-hazard/].
MMI10
15
Refrences
Colton, R.B., 1978, Geologic map of the Boulder–Fort Collins–Greeley area, Front Range Urban Corridor, Colorado: U.S. Geological Survey Miscellaneous Investigations Map I-855-G, scale 1:100,000 [Available at https://pubs.er.usgs.gov/publication/i855G/].
MMI11
16
Refrences
Colton, R.B., and Fitch, H.R., 1974, Map showing potential sources of gravel and crushed-rock aggregate, in the Boulder–Fort Collins–Greeley area, Front Range Urban Corridor, Colorado: U.S. Geological Survey Miscellaneous Investigations Map I-855-D, scale 1:100,000 [Available at https://pubs.er.usgs.gov/publication/i855D/].
MMI12
17
Refrences
Crabb, J.A., 1980, Soil survey of Weld County, Colorado, southern part: U.S. Department of Agriculture, U.S. Soil Conservation Service, Washington, DC, 135 p., 35 maps, scale 1:24,000.
MMI13
18
Refrences
Dechesne, M., Raynolds, R.G., Barkmann, P.E., and Johnson, K.R., 2011, Notes on the Denver Basin geologic maps: Bedrock geology, structure, and isopach maps of the Upper Cretaceous to Paleocene Strata between Greeley and Colorado Springs: Colorado Geological Survey Open File Report 11-01, 35 p. [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-stratigraphy-notes-denver-basin-colorado/].
MMI14
19
Refrences
Empire Laboratories Inc., 1985, Report of a geologic investigation for a portion of Beebe Draw Farms Weld County, Colorado. Project no. 142C-85: Colorado State Archives, Document ID WE-84-0013.
MMI15
20
Refrences
Duller, R.A., Whittaker, A.C., Swinehart, J.B., Armitage, J.J., Sinclair, H.D., Blair, Andrea, and Allen, P.A., 2012, Abrupt landscape change post-6 Ma on the central Great Plains, USA: Geology, v. 40. no. 10, p. 871–874.
MMI16
21
Refrences
Fenneman, N.M., 1931, Physiography of western United States: New York, McGraw-Hill Book Co, 534 p.
MMI17
22
Refrences
Fishman, N.S., 2005, Overview of studies related to energy resources, northern Front Range, Colorado, p. 1-8, in Fishman, N.S. ed., Ch. A: Energy resource studies, northern Front Range, Colorado: U.S. Geological Survey Professional Paper 1698, 162 p. [Available at https://pubs.usgs.gov/pp/2005/1698/].
MMI18
23
Refrences
Forman, S.L., Tew-Todd, V., Mayhack, C., Marin, L., Wiest, L.A., and Money, G., 2022 Late Quaternary aeolian environments, luminescence chronology and climate change for the Monahans dune field, Winkler County, West Texas, USA: Aeolian Research, v. 58, 100828.
MMI19
24
Refrences
Forman, S.L., and Maat, P., 1990, Stratigraphic evidence for late Quaternary dune activity near Hudson on the Piedmont of northern Colorado: Geology, v. 18, p. 745-748.
MMI20
25
Refrences
Galbraith, R.F., and Roberts, R.G., 2012, Statistical aspects of equivalent dose and error calculation and display in OSL dating: An overview and some recommendations: Quaternary Geochronology, v. 11, p. 1-27.
MMI21
26
Refrences
Galbraith, R.F., and Green, P.F., 1990, Estimating the component ages in a finite mixture: International Journal of Radiation Applications and Instrumentation, v. 17, p. 197-206.
MMI22
27
Refrences
Hansen, W.R., and Crosby, E.J., 1982, Environmental geology of the Front Range urban corridor and vicinity, Colorado: U.S. Geological Survey Professional Paper 1230, 99 p. [Available at https://pubs.er.usgs.gov/publication/pp1230/].
MMI23
28
Refrences
High Plains Engineering, 2005, Subsurface investigation and foundation recommendations: Colorado State Archives, Document ID WE-06-0003.
MMI24
29
Refrences
Hillier, D.E., and Schneider, P.A. Jr., 1979, Well yields and chemical quality of water from water-table aquifers in the Boulder-Fort Collins-Greeley area, Front Range urban corridor, Colorado: U.S. Geological Survey Miscellaneous Investigation Series Map I-855-J, scale 1:100,000 [Available at https://pubs.usgs.gov/publication/i855J/].
MMI25
30
Refrences
Horizon Construction Service, 2000, Geotechnical investigation report of Beebe Draw Farms and Equestrian Center, filing 2, located in sections 4, 5, 8, 9, 10, and 17, township 3 north, range 65 west of the 6th principal meridian, Weld County, Colorado, for Beebe Draw Farms Metropolitan District, 11409 West 17th Place, Lakewood, Colorado 80215: Colorado State Archives, Document ID WE-00-0049.
MMI26
31
Refrences
Hunt, C.B., 1954, Pleistocene and recent deposits in the Denver area, Colorado: U.S. Geological Survey Bulletin 996-G, p. 91-140 [Available at https://pubs.er.usgs.gov/publication/b996C/].
MMI27
32
Refrences
International Union of Geological Sciences, 2022, International Commission on Stratigraphy, version 2022/10 [Available at https://stratigraphy.org/chart/].
MMI28
33
Refrences
Keller, S.M., and Marr, A.E., 2023, Geologic map of the Valley View School quadrangle, Weld County, Colorado: Colorado Geological Survey Open-File Report 21-02, scale 1:24,000 [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-valley-view-school-quadrangle-weld-colorado/].
MMI29
34
Refrences
Keller, S.M., 2023, Eolian fine-grained sediment in the northern Colorado Piedmont: Geological Society of America Abstracts with Programs, v. 55, no. 55.
MMI30
35
Refrences
Kellogg, K.S., Shroba, R.R., Bryant, Bruce, and Premo, W.R., 2008, Geologic map of the Denver West 30′ × 60′ quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3000, scale 1:100,000 [Available at https://pubs.er.usgs.gov/publication/sim3000/].
MMI31
36
Refrences
Kirkham, R.M., and Ladwig, L.R., 1979, Coal resources of the Denver and Cheyenne Basins, Colorado: Colorado Geological Survey Resource Series RS-5, 76 p. [Available at https://coloradogeologicalsurvey.org/publications/coal-resources-denver-cheyenne-basins-colorado/].
MMI32
37
Refrences
Kocurek, G., 1981, Significance of interdune deposits and bounding surfaces in aeolian dune sands: Sedimentology, v. 28, p. 753-780.
MMI33
38
Refrences
Leonard, E.M., 2002, Geomorphic and tectonic forcing of the Cenozoic warping of the Colorado Piedmont: Geology, v. 30, no. 7, p. 595-598.
MMI34
39
Refrences
Liang, P., and Forman, S.L., 2019, LDAC: An Excel-based program for luminescence equivalent dose and burial age calculations: Ancient TL, v. 37, p. 21–40.
MMI35
40
Refrences
Lindsey, D.A., Langer, W.H., and Knepper, D.H., Jr., 2005, Stratigraphy, lithology, and sedimentary features of Quaternary alluvial deposits of the South Platte River and some of its tributaries east of the Front Range, Colorado: U.S. Geological Survey Professional Paper 1705, 70 p. [Available at https://pubs.er.usgs.gov/publication/pp1705/].
MMI36
41
Refrences
Machette, M.N., 1985, Calcic soils of the southwestern United States, in Soils and quaternary geology of the southwestern United States, D.L. Weide and M.I. Faber, eds: Geological Society of America Special Paper 203, p. 1-21.
MMI37
42
Refrences
Madole, R.F., 2016, Geologic map of the Longmont quadrangle, Boulder and Weld Counties, Colorado: Colorado Geological Survey Open-File Report 16-05, scale 1:24,000 [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-longmont-quadrangle-boulder-weld-colorado/].
MMI38
43
Refrences
Madole, R.F., VanSistine, D.P., and Michael, J.A., 2005, Distribution of late Quaternary wind-deposited sand in eastern Colorado: U.S. Geological Survey Scientific Investigations Map 1725, 49 p., scale 1:700,000 [Available at https://pubs.er.usgs.gov/publication/sim2875/].
MMI39
44
Refrences
Madole, R.F., 1995, Spatial and temporal patterns of late Quaternary eolian deposition, eastern Colorado, U.S.A.: Quaternary Science Reviews, v. 14, p. 155-177.
MMI40
45
Refrences
Madole, R.F., 1991, Colorado Piedmont, in Wayne, W.J., ed., Quaternary geology of the Northern Great Plains, Chap.15 of Morrison, R.B., ed., Quaternary nonglacial geology -conterminous United States: Geological Society of America, The geology of North America, v. K-2, p. 456-462.
MMI41
46
Refrences
Marder, E., Gallin, S.F., and Pazzaglia, F.J., 2023, Late Cenozoic deformation in the U.S. southern Colorado Front Range revealed by river profile analysis and fluvial terraces: Geological Society of America Bulletin, v. 136, n. ¾, p. 1067-1085.
MMI42
47
Refrences
Muhs, D.R., Aleinikoff, J.N., Stafford , T.W., Jr., Been, J., Mahan, S.A., and Cowherd, S., 1999, Late Quaternary loess in northeastern Colorado, Part I - Age and paleoclimatic significance: Geological Society of America Bulletin, v. 111, n. 12, p. 1861-1875.
MMI43
48
Refrences
Munsell Color, 1991, Munsell soil color charts, 1990 edition revised: Newburgh, NY, Macbeth Division of Kollmorgan Instruments Corp.
MMI44
49
Refrences
Murray, A.S., and Wintle, A.G., 2003, The single aliquot regenerative dose protocol: potential for improvements in reliability: Radiation Measurements, v. 37, p. 377-381.
MMI45
50
Refrences
Nichols, G., 2009, Sedimentology and stratigraphy (second edition): Wiley-Blackwell, Chichester (United Kingdom), 419 p.
MMI46
51
Refrences
Odom, W.E., Ruleman, C.A., Sterne, E., O’Keefe, M., and Morgan, M., 2024, Cosmogenic Al-26/Be-10 isochron burial date for the Nussbaum Gravel at Baculite Mesa, CO: U.S. Geological Survey data release. [Available at https://www.usgs.gov/data/cosmogenic-al-26be-10-isochron-burial-data-nussbaum-gravel-baculite-mesa-co/].
MMI47
53
Refrences
O’Keeffe, M.K., and Berry, K.A., 2021, Colorado mineral and energy industry activities 2019-2020: Colorado Geological Survey Information Series 83, 36 p. [Available at https://coloradogeologicalsurvey.org/publications/colorado-mineral-energy-industry-activities-2020/].
MMI48
54
Refrences
O’Keeffe, M.K., Morgan, M.L., Keller, S.M., Horkley, K.L., and Keller. J.W., 2018, Reconnaissance of potential sand sources in Colorado for hydraulic fracturing resource: Colorado Geological Survey Resource Series 47, 38 p. [https://coloradogeologicalsurvey.org/publications/potential-sand-sources-hydraulic-fracturing/].
MMI49
55
Refrences
Palkovic, M.J., Lindsey, K.L., and Morgan, M.L., 2019, Geologic map of the La Salle quadrangle, Weld County, Colorado: Colorado Geological Survey Open-File Report 19-03, scale 1:24,000 [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-la-salle-quadrangle-weld-colorado/].
MMI50
56
Refrences
Palkovic, M.J., Lindsey, K.L., and Morgan, M.L., 2018, Geologic map of the Milliken quadrangle, Weld County, Colorado: Colorado Geological Survey Open-File Report 18-02, scale 1:24,000 [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-milliken-quadrangle-weld-colorado/].
MMI51
57
Refrences
Palkovic, M.J., and Morgan, M.L., 2017, Geologic map of the Johnstown quadrangle, Weld and Larimer Counties, Colorado: Colorado Geological Survey Open-File Report 17-02. Scale 1:24,000 [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-johnstown-quadrangle-larimer-weld-colorado/].
MMI52
58
Refrences
Prescott, 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
59
Refrences
Ramsey, C.B., 2009, Bayesian analysis of radiocarbon dates: Radiocarbon, v. 51, p. 337-360.
MMI54
60
Refrences
Raynolds, R.G., Cretaceous stratigraphy of Colorado: Colorado Geological Survey Map Series 54 [Available from at https://coloradogeologicalsurvey.org/publications/cretaceous-stratigraphy-colorado/].
MMI55
61
Refrences
Reimer, P.J., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Ramsey, C.B., Buck, C.E., Cheng, H., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P., Haflidason, H., Hajdas, I., Hatte, C., Heaton, T.J., Hoffmann, D.L., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., Manning, S.W., Niu, M., Reimer, R.W., Richards, D.A., Scott, E.M., Southon, J.R., Staff, R.A., Turney, C.S.M., and Van der Plicht, J., 2013, IntCal13 and Marine13 radiocarbon age calibration curves, 0–50,000 years cal B.P.: Radiocarbon, v. 55, no. 4, p.1869–1887.
MMI56
62
Refrences
Riihimaki, C.A., Anderson, R.S., Safran, E.B., Dethier, D.P., Finkel, R.C., and Bierman, P.R., 2006, Longevity and progressive abandonment of the Rocky Flats surface, Front Range, Colorado: Geomorphology, v. 78, p. 265-278.
MMI57
63
Refrences
Robson, S.G., Heiny, J.S., and Arnold, L.R., 2000, Geohydrology of the shallow aquifers in the Fort Lupton-Gilcrest area, Colorado: U.S. Geological Survey Hydrologic Atlas 746-C [Available at https://pubs.er.usgs.gov/publication/ha746C/].
MMI58
64
Refrences
Robson, S.G., 1996, Geohydrology of the shallow aquifers in the Denver metropolitan area, Colorado: U.S. Geological Survey Hydrologic Investigations Atlas HA-736, scale 1:50,000 [Available at https://pubs.er.usgs.gov/publication/ha736/].
MMI59
65
Refrences
Scott, G.R., 1982, Paleovalley and geologic map of northeastern Colorado: U. S. Geological Survey, Map I-1378 [Available at https://pubs.er.usgs.gov/publication/i1378/].
MMI60
66
Refrences
Scott, G.R., 1963, Quaternary geology and geomorphic history of the Kassler quadrangle, Colorado: U.S. Geological Survey Professional Paper 421-A, 74 p. [Available at https://pubs.er.usgs.gov/publication/pp421A/].
MMI61
67
Refrences
Shawe, D.R., Steven, T.A., and Knepper. Jr., D.H., 2008, Possible young faulting in the piedmont of north-central Colorado: The Mountain Geologist, v. 45, no. 1, p. 1-79.
MMI62
68
Refrences
Schwochow, S.D., Shroba, R.R., and Wicklein, P.C., 1974, Sand, gravel, and quarry aggregate resources, Colorado Front Range counties: Colorado Geological Survey Special Publication 5-A, 48 p. [Available at https://coloradogeologicalsurvey.org/publications/sand-gravel-quarry-aggregate-colorado-front-range/].
MMI63
69
Refrences
Smith, J.J., Layzell, A.L., Lukens, W.F., Morgan, M.L., Keller, S.M., Martin, R.A., and Fox, D.L., 2016, Getting to the bottom of the High Plains aquifer - New insights into the depositional history, stratigraphy, and paleoecology of the Cenozoic High Plains in Keller, S.M., and Morgan, M.L., eds., Unfolding the geology of the West; Geological Society of America Field Guide 44, p. 93-124.
MMI64
70
Refrences
Smith, R.O., Schneider, P.A., Jr., and Petri, L.R., 1964, Ground-water resources of the South Platte River basin, western Adams and southwest Weld Counties Colorado: Geological Survey Water-Supply Paper 1658, 132 p. [Available at https://pubs.er.usgs.gov/publication/wsp1658/].
MMI65
71
Refrences
Soister, P.E., 1965a, Geologic map of the Fort Lupton quadrangle, Weld and Adams Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-397, scale 1:24,000 [Available at https://pubs.er.usgs.gov/publication/gq397/].
MMI66
72
Refrences
Soister, P.E., 1965b, Geologic map of the Hudson quadrangle, Weld and Adams Counties, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-398, scale 1:24,000 [Available at https://pubs.er.usgs.gov/publication/gq398/].
MMI67
73
Refrences
Soister, P.E., 1965c, Geologic map of the Platteville quadrangle, Weld County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-399, scale 1:24,000 [Available at https://pubs.er.usgs.gov/publication/gq399/].
MMI68
74
Refrences
Topper, R., Spray, K.L., Bellis, W.H., Hamilton, J.L., and Barkmann, P.E., 2003, Ground Water Atlas of Colorado: Colorado Geological Survey Special Publication 53, 210 p. [Available at https://coloradogeologicalsurvey.org/water/colorado-groundwater-atlas/].
MMI69
75
Refrences
Turney, J.E., and Murray-Williams, L., 1983, Colorado Front Range inactive coal mine data and subsidence information, Weld County, Plate 12 of 12: Colorado Geological Survey unpublished map prepared in 1983, scale 1:50,000.
MMI70
76
Refrences
U.S. Department of Agriculture, Natural Resources Conservation Service, 2018, Assessing carbonates in the field with a dilute hydrochloric acid solution: Soil Survey Technical Note 5, 7 p.
MMI71
77
Refrences
White, J.L., and Greenman, C., 2008, Collapsible soils in Colorado: Colorado Geological Survey Engineering Geology 14, 108 p. [Available at https://coloradogeologicalsurvey.org/2018/28848-collapsible-soils/].
MMI72
78
Refrences
Wintle, A.G., and Murray, A.S., 2006, A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols: Radiation Measurements, v. 41, p. 369-391.
MMI73
79
References
Wray, L.L., and Koenig, N.V., 2001, The coalbed methane potential in the Upper Cretaceous to Early Tertiary Laramie and Denver Formations, Denver Basin, Colorado: Colorado Geological Survey Open-File Report 01-17, 88 p. [Available at https://coloradogeologicalsurvey.org/publications/coalbed-methane-potential-cretaceous-tertiary-laramie-formations-denver-basin-colorado/].
MMI74
80
References
O’Keeffe, M.K., 2024, Colorado mineral and energy industry activities 2022-2023: Colorado Geological Survey Information Series 86, 32 p. [Available at https://coloradogeologicalsurvey.org/publications/colorado-mineral-energy-industry-activities-2023/].
MMI75
81
References
Cappa, J.A., and TerBest, H., 2002, Evaluation of mineral and mineral fuel potential of Weld County, State Mineral Lands administered by the Colorado State Land Board: Colorado Geological Survey Open-File Report 02-23, p. 11-12 [Available at https://coloradogeologicalsurvey.org/publications/evaluation-mineral-fuel-potential-weld-cslb/].
MMI76
Database Inventory
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