The database-level FGDC metadata are formally correct
although the metadata record should be reviewed to verify that it is meaningful.
This file should be accompanied by OF-24-03_Severance.gdb-ValidationErrors.html and OF-24-03_Severance-metadata.xml_errors.txt
in the same directory.
If this database will be submitted to the NGMDB, it also needs to be accompanied by
a reviewed Geologic Names report that includes identification of any suggested modifications to Geolex. Use the
Geologic Names
Check tool to generate that report or provide other documentation of a review.
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.
Isotope Geology Laboratory at Boise State University
None
https://www.boisestate.edu/earth-isotope/
BOISE
2
This study
None
None
DAS1
5
Online dictionary
None
https://dictionary.com/
DICT1
6
Wikipedia
None
https://en.wikipedia.org/
DICT2
7
Colorado Division of Water Resources (DWR)
None
https://dwr.colorado.gov/
DWR
8
Colorado Energy and Carbon Management Commission (ECMC)
None
https://ecmc.colorado.gov/
ECMC
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
3
GeMS standard
None
https://ngmdb.usgs.gov/Info/standards/GeMS/
GEMS1
4
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
Label
Symbol
ParagraphStyle
HierarchyKey
Age
Description
GeoMaterial
GeoMaterialConfidence
AreaFillRGB
AreaFillPatternDescription
DescriptionSourceID
DescriptionOfMapUnits_ID
1
None
DMU HEADER
DESCRIPTION OF MAP UNITS
DESCRIPTION OF MAP UNITS
None
DMUHeading1
01
None
None
None
None
None
None
DAS1
DMU01
2
None
DMU SUMMARY
DMU SUMMARY
DMU SUMMARY
None
DMUUnit1
01-01
None
A summary of the geological history, mineral and groundwater resources, and geologic hazards can be found on Plate 2. Division of geological time follows the International Chronostratigraphic Chart (International Union of Geological Sciences, 2023). For grain size categories, refer to the Udden-Wentworth grain-size in Nichols (2009). Descriptions of the soil colors and carbonate development are based on Munsell (1991) and Machette (1985), respectively. Relative amounts of calcium carbonate (CaCO3) are interpreted based on the degree of effervescence in soil or sediment when treated with diluted (10%) hydrochloric acid (HCl) according to the U.S. Department of Agriculture (2018).
None
None
None
None
DAS1
DMU02
3
None
SURFICIAL DEPOSITS HEADER
SURFICIAL DEPOSITS
SURFICIAL DEPOSITS
None
DMUHeading1
02
None
None
None
None
None
None
DAS1
DMU03
4
None
HUMAN-MADE DEPOSIT HEADER
HUMAN-MADE DEPOSITS
HUMAN-MADE DEPOSITS
None
DMUHeading2
02-01
None
None
None
None
None
None
DAS1
DMU04
5
af
Artificial Fill
Artificial Fill
af
af
DMUUnit1
02-01-01
uppermost Holocene
Artificial fill (uppermost Holocene) — The unit is comprised of mostly fill material, riprap, and refuse in the construction of dams, roads, buildings, and landfill. Deposits are generally made up of unsorted clay, silt, sand, and rock fragments. Typically, the unit is less than 6 m thick. Artificial fill may be subjected to settlement, slumping, and erosion if not adequately compacted.
"Made" or human-engineered land
High
255-255-255
None
DAS1
DMU05
6
None
EOLIAN DEPOSITS HEADER
EOLIAN DEPOSITS
EOLIAN DEPOSITS
None
DMUHeading2
02-02
None
None
None
None
None
None
DAS1
DMU06
7
Qe
Eolian Sediment
Eolian Sediment
Qe
Qe
DMUUnit1
02-02-02
Holocene to Upper Pleistocene
Eolian Sediment (Holocene to Upper Pleistocene) — The unit is comprised of very-pale brown to yellowish-brown and light-olive brown (10YR and 2.5Y) massive, loose to stiff, moderate to well-sorted, very fine to medium-grained sand with minor to trace coarse and very coarse-grained sand. Sand grains are mainly subrounded to rounded and are compositionally comprised of 75-80% quartz, 14-25% feldspar and other minerals, and 0-7% opaque minerals. Locally, unit Qe may contain bedrock fragments. West of the Weld County Road (WCR) 27 and 72 junction, the authors observed fossiliferous sandstone fragments from underlying unit Kp bedrock ranging in length from 3 mm to 5 cm in the edge of a silage pit. In an irrigation ditch wall west of WCR 76 and 27 junction, a boulder size bedrock fragment (unit Kp) about 0.5-1 m in diameter was observed in unit Qe. Unit Qe may also locally have sheetwash deposits, especially on the edges of valleys and on relatively steep slopes. According to Cross Section B, unit Qe ranges from about 2-14 m thick. Some of this thickness could very well be due in part to weather bedrock, deposits of sheetwash alluvium or colluvium.
Unit Qe has moderate to strong effervescence when treated with diluted hydrochloric acid (HCl). Secondary calcic carbonate development in this unit can range from none to Bk carbonate horizons as large as 1.2 m and carbonate nodules around < 1 mm thick (Stage I). In addition to carbonate horizons, older Qe units may also have Bt horizons that can range approximately from 0.1-0.6 m thick.
Locally, some deposits may have a higher fines (silt and clay) content. Based on grain size analyses from geotechnical reports throughout the Severance area, the fines content in unit Qe ranges from 21-69%. While the average fines content ranges from around 30-40%, this unit can be classified as loess when it is > 60% (Muhs and others, 2014).
The age of unit Qe in the Severance quadrangle area is mostly Holocene but can be as old as Upper Pleistocene. Two radiocarbon (14C) samples of this unit (SV019CC14 and SV032C14, see Table 1) were collected in this investigation and yielded age estimates of 8,770 ± 30 and 7,440 ± 30 calibrated years before present (cal. yrs BP), respectively. Other dates for eolian sediment from the surrounding Greely, Windsor, and Timnath quadrangles range from about 820-9,280 cal. yrs BP (Keller and Morgan, 2020; Keller and Marr, 2024; Perman and others, 2025). On the eastern shore of Black Hollow Reservoir, unit Qe is silty, fine- to medium-grained sand about 1.6 m-thick and overlays the Pierre Shale (unit Kp). At the base of unit Qe are rare gravel as large as 2.5 cm pebbles. A 60 cm-thick Bt soil horizon has developed into this unit with columnar structure. At the same location, multiple clastic dikes, resembling ice wedges, are present where the overlying unit Qe infilled wedge-shaped spaces in the underlying unit Kp, forming sand wedges ranging in size from about 4-30 cm in width. Ice wedges, formed by periglacial processes, have been reported in Wyoming, including the Laramie and Cheyenne areas (Mears, 1981; Nissen, 1985) and at the Anton Escarpment about 200 km southeast of the Severance quadrangle (Noe, 2010). Two OSL samples from unit Qe were taken from the eastern shore of Black Hollow (see Table 2): one near the contact of overlaying unit Qe and Kp (SV086OSL), and one from a sand wedge (SV086AOSL). The sample from the overlaying Qe (SV086OSL) yielded an age of 13,860 ± 645 SAR-OSL years and the sand wedge (SV086AOSL) yielded an age of 13,755 ± 685 SAR-OSL years. However, both samples have an overdispersion percentage > 20%, indicating that this estimate may not be the true deposition age and may have been reworked due to partial solar resetting and/or multiple grain populations (Baylor University, 2025). Ages of the ice wedges from the Anton Escarpment indicated that there were three distinct periods of permafrost ice-wedge formation which occurred from 27.5-18 ka, 20-16 ka, and older wedges with dates around 42.5 and 130 ka based on OSL dates (Noe, 2010). Depending on the silt and clay content, this deposit can contain expansive and/or collapsible soils, which can impact future and existing buildings and infrastructure if not properly mitigated.
Eolian sediment
Medium
255-255-178
None
DAS1
DMU07
8
None
ALLUVIAL DEPOSITS HEADER
ALLUVIAL DEPOSITS
ALLUVIAL DEPOSITS
None
DMUHeading2
02-03
None
None
None
None
None
None
DAS1
DMU08
9
Qa
Alluvium, undivided
Alluvium, undivided
Alluvium, undivided
Qa
DMUUnit1
02-03-01
Holocene
Alluvium, undivided (Holocene) — Unit Qa is mapped in The Slough, Coalbank Creek valleys, and overlays portions of the “Eaton” paleovalley (named by Robson and others, 2000a) based on lidar imagery, and two feet contours from digital elevation map (DEM) imagery. In the Severance quadrangle, unit Qa is locally covered and intermixed with eolian sediment (unit Qe).
Overlaying the “Eaton” paleovalley by WCR 88 and 29, the alluvium is a grayish brown (10 YR), well-sorted, silty clay or clayey silt sand with moderate effervescence. The sand content is roughly 40-50% and fine grained. Further downstream by WCR 86, from an excavated pond, the unit is more gravel rich, comprising 20-30% of the deposit. Grains range in size from granules to 3.5 cm pebbles and are subangular to subrounded. Some of the pebbles have thin carbonate coating (< 1 mm-thick) that are most likely reworked from units Qg and Qg2. Based on water wells (CO DWR, 2023), the alluvium overlaying the “Eaton” paleovalley is about 9 to 12 m-thick but be up to 18 m-thick.
In the Coalbank Creek valley, unit Qa is a moderately well to poorly sorted pale brown and brown (10YR) gravelly sand with local high fines content. The sand is very fine- to coarse-grained and either does not effervesce or effervescences slightly with HCl. The gravel comprises 20-30% of the deposit. Clasts are typically subangular to rounded and range in size from granules to 3 cm pebbles but can be as large as 17 cm cobbles in length. Gravel clasts are primarily comprised of granitic rocks, gneiss, vein quartz, white quartzite, and possible blue quartzite from Coal Creek (see Lindsey and others, 2005). Some of the gravel has carbonate coatings and could also possibly be reworked from units Qg and Qg2. Water well logs from CO DWR (2023) show that the thickness of alluvium in Coalbank Creek is about 8-9 m. According to Colton (1978), the alluvium in Coalbank Creek correlates to the Piney Creek Alluvium which has been mapped as unit Qa2 in other nearby Colorado Geological Survey maps. In the surrounding Greeley, Windsor, and Timnath quadrangles, the ages of unit Qa2 range from 1,910-4,360 calibrated year BP (Keller and Morgan, 2020; Keller and Marr, 2024; Perman and others, 2025).
In The Slough valley, south of the town of Severance, unit Qa occurs along the cutbank of the modern channel as a pale brown (10YR), moderately well sorted, silty gravelly sand with none to slight effervescence when treated with HCl. CaCO3 filaments up to 1 mm-thick are present locally. Sand grains are mostly subangular to subrounded and very fine- to fine-grained, with local medium- to coarse-grained sand. Although not seen in-situ, gravel clasts were observed from shallow trenching (depth approximately 30 cm) near the margin of The Slough modern channel at the Severance Community Park (see SV018C14 on Plate 1). The observable gravel clast content is 10% of the sediment and ranges in size from granules to 2 cm pebbles. Another alluvium facies that was observed, but not in-situ, was a gray (10YR) well sorted very fine to fine sand, no visible carbonate development, and has rare bedding at millimeter scale. A C14 sample was taken near the Severance Community Park (SV018C14, see Table 1) and yielded an age of 1,170 ± 30 cal. yrs BP. According to McComas (1966), the grain size distribution of the alluvium underlying The Slough valley is about 25.1% granules, 8.3% very coarse-sand, 6.8% coarse sand, 16.8% medium sand, 21.8% fine sand, 17% very fine-sand, and 4.2% silt. Unit Qa in The Slough valley and around the town of Severance is 6-10 m thick but can be up to 15 m thick (CO DWR, 2023). Unit Qa may contain expansive and/or collapsable soil depending on silt and clay content. Areas underneath unit Qa may be prone to flooding; the valleys of The Slough, Coalbank Creek, and western portion of the “Eaton” paleovalley are designated as 100-year floodplains by the Federal Emergency Management Agency (FEMA, 2023).
Eolian sediment
Medium
255-255-102
ESRI 24k Geology 601 Gravel 215-176-158
DAS1
DMU09
10
Qg1
Gravel deposit one
Gravel deposit one
Qg1
Qg1
DMUUnit1
02-03-02
Middle Pleistocene?
Gravel deposit one (Middle Pleistocene?) — Unit Qg1 was observed exclusively along the eastern shores of Black Hollow Reservoir. At this location, unit Qg1 was initially deposited within a paleogeographic stream channel where an ancestral creek scoured and incorporated portions of the underlying Kp and PENbh units into the deposits. The unit consists of pale brown to light yellowish gray (2.5Y), moderately to poorly sorted gravelly sand with interbedded layers of sandy silt and clay. The sand grains are predominantly very fine to medium, with minor amounts of coarse to very coarse grains, and are subangular to subrounded.
Gravel content constitutes between 5% and 60% of the unit, ranging in size from granules to 12.5 cm cobbles in diameter, with most clasts measuring approximately 5 cm in diameter. The gravel is primarily subangular to subrounded and comprised of dark-colored metamorphic and igneous rocks, brown sandstone, and granitic rocks; some clasts are comprised entirely of potassium feldspar. Bedding on the millimeter scale was observed within this unit. Soils developed into this unit have included Stage I-II CaCO3 morphology. Carbonate nodules up to 5 mm in diameter, filaments up to 2 cm-long and 1-mm thick, and discontinuous, lobate-shaped filaments up to 4 cm-long are present in the matrix. Some clasts have carbonate coatings up to about 1 mm-thick, and the matrix effervesces weakly to violently.
Three samples were collected for OSL analyses (see Table 2). Two samples were collected from a single exposed face about 1.1 and 0.76 m below ground surface near the top of the deposit. A third sample was collected from a different exposure 50 m to the east. The highest sample from the first site (SV085B2.5OSL) was collected near the bottom of a 0.6 m thick gravelly sand layer below a 10 cm thick Bt soil horizon and yielded an infinite age of greater than 304 ka SAR OSL years. The second sample (SV085B3.5OSL) was collected about 0.3 m below the highest sample and yielded an age of 73,810 ± 7820 SAR OSL years. The results of these are stratigraphically reversed. The third sample site (SV085A3.4OSL) nearby was collected from about 1 m below the surface in a 80 cm thick gravelly sand layer below a 30 cm Bt soil horizon and yielded an age of 7,685 ± 210 SAR OSL years.
Given the observed Stage I-II carbonate development overlying the sample, it is likely that 7,685 ± 210 estimate is too young. The 73,810 ± 7,820 year age estimate seems more reasonable due to the soil development (Bk and Bt horizons), position above The Slough valley, and its poor preservation. Even though the result is infinite, the > 304 ka estimate could also be supported by these observations. In the surrounding quadrangles, the CGS has mapped and collected OSL age dates unit Qg1. Results in the Valley View School and Timnath quadrangles provided age estimates of about 341 ka and 133 ka SAR OSL, respectively (Keller and Marr, 2023; Perman and others, 2025). This unit is possibly correlative to the Slocum Alluvium which was mapped by the USGS in the past. In the Denver area, Slocum Alluvium is estimated to be about 300 and 220 ka, and possible older deposits are around 390 and 320 ka (Kellogg and others, 2008). Apart from the greater than 304 ka estimate, the age results collected from Black Hollow Reservoir are
Alluvial sediment, mostly coarse-grained
Medium
255-255-215
115-255-223 ESRI geology 24k 601 Gravel, open
DAS1
DMU10
11
Qg2
Gravel deposit two
Gravel deposit two
Qg2
Qg2
DMUUnit1
02-03-03
Middle Pleistocene
Gravel deposit two (Middle Pleistocene) — The unit is comprised of very pale brown to light brown and white (10 YR and 7.5 YR), poorly to very poorly sorted, very fine- to very coarse-grained sand with gravel with minor fines. Sand grains are mainly subangular to subrounded and comprise 75% quartz, 25% feldspar and other minerals, and < 1% opaque minerals. Gravel clasts range from angular to well-rounded but are generally subrounded. The lithology of the clasts includes granitic rock, brown sandstone, gneissic rock, and possible ironstone concretions. While the gravel content observed during this investigation ranges from approximately 3-50%, Colton and Fitch (1974) conducted a grain size analysis of unit Qg2 in the northern part of the Severance quadrangle. The analysis estimates the unit is 40-70% gravel and 30-40% sand, and 10-30% clay and silt. Clasts range in size from granules to 16 cm cobbles but can be as large as 37 cm boulders. By the WCR 84 and 25 junction, a soil developed into a silty gravelly sand deposit has a moderately to strongly cemented K horizon with Stage III to IV carbonate morphology. Secondary carbonate nodules in the matrix are as much as 3 mm in diameter and gravel clast coatings were observed at least 1 mm-thick. The thickness of unit Qg2 ranges from 2-9 m in the greater Fort Collins area (Workman and others, 2018). The unit is locally overlain by unit Qe and has been heavily modified by pedogenic processes.
Unit Qg2 is the oldest surficial deposit in the Severance quadrangle. Colton (1978) mapped this unit as Verdos Alluvium based on the unit’s height above local major streams (60-75 m). In the Denver area, the Verdos Alluvium at several locations the Lava Creek B ash from Yellowstone has been deposited within the top and middle of the unit and locally at the base (Kellogg and others, 2008). This ash has been dated to about 631 ka (Matthews and others, 2015) but locally may include younger deposits about 475-410 ka (Kellogg and others, 2008). Unit Qg2 is a potential source of local sand and gravel.
Alluvial sediment, mostly coarse-grained
Medium
255-255-215
0-112-255 ESRI geology 24k 601 Gravel, open
DAS1
DMU11
12
Qg
Gravel undivided
Gravel undivided
Qg
Qg
DMUUnit1
02-03-04
Middle Pleistocene?
Gravel undivided (Middle Pleistocene?) — Shown in cross-section only. The unit primarily consists of old gravel alluvium mantled by eolian deposits. It was previously mapped as a terrace deposit along The Slough by McComas (1966), as the Verdos Alluvium by Colton (1978) north of the town of Severance, and as the sand and gravel deposits of the “Eaton” paleovalley (Robson and others, 2000a). Based on Cross Section B derived from water well logs, the thickness of unit Qg in the “Eaton” paleovalley ranges from approximately 2.7 to 11.9 m and is overlain by 2.4 to 7 m of eolian sediment (unit Qe). Additionally, this unit includes sand and gravel deposits identifiable in water well logs (CO DWR, 2023) on the highlands between The Slough and Coalbank Creek valleys, which were not previously mapped. These deposits are typically 3 to 8 m thick but can locally thin to less than 1 m.
Although not directly observed during this study, McComas (1966) described unit Qg (referred to as unit Qt in his work) in The Slough near the town of Severance. He noted that the gravel in unit Qg ranges in size from around 1 cm and is cemented by CaCO3. The thickness of the gravel layers ranges from 15 to 46 cm. Within the gravel, there are interbedded layers of white to light gray calcareous clay and highly organic dark brown to black clay (possible paleosols or overbank deposits), each approximately 0.6 m thick. The overall thickness of unit Qg north of the town of Severance is estimated to range from 1 to 13 m, based on Cross Section B. Based on the carbonate development described by McComas (1966) described above, the age of this unit is likely Middle Pleistocene.
Alluvial sediment, mostly coarse-grained
Medium
255-255-215
255-170-0 ESRI geology 24k 601 Gravel, open
DAS1
DMU12
13
Qcs
Colluvium and sheetwash deposits, undivided
Colluvium and sheetwash deposits, undivided
Qcs
Qcs
DMUUnit1
02-03-05
Holocene to Upper Pleistocene
Colluvium and sheetwash deposits, undivided (Holocene to Upper Pleistocene) — Unit Qcs occurs along the valley sides of The Slough and Coalbank Creek in the northern part of the quadrangle, where bedrock is shallow. It is also present west of the WCR 25 and Hwy 14 junction, where it occupies a bowl-shaped landform. The unit is not well exposed; however, it forms distinct coalescing fans and aprons at the base of the bedrock and base of unit Qg2 as seen in lidar imagery.
Colluvium within unit Qcs consists of bedrock fragments and local gravel derived from unit Qg2 that have been transported downslope by gravity. In the Coalbank Creek valley, sheetwash deposits are moderately sorted, brown, very fine to medium sand with minor gravel, as well as poorly sorted, pale brown sandy gravel. Gravel within this deposit ranges in size from granules to 6 cm pebbles, with larger local cobbles and boulders. A radiocarbon sample, SV104C14 (see Table 1), was taken from unit Qcs fan in the Coalbank Creek Valley, yielding a 14C conventional age of 500 ± 30 years. In The Slough valley, based on water wells from CO DWR (2023), the sheetwash deposits consist of brown and light yellowish-brown sandy clay.
Unit Qcs may include sediments from minor gullies and rills, local bedrock residuum, reworked eolian sediments, and may grade into or interfinger with units Qa and Qe. Based on water well data from CO DWR (2023), the thickness of unit Qcs typically ranges from 5-7 m but can be as thick as 11 m. Areas mapped as unit Qcs are locally susceptible to small debris flows and swelling or collapsing soils. This unit may also serve as a local source of sand and gravel for fill material.
Alluvial sediment, mostly coarse-grained
Medium
226-236-185
None
DAS1
DMU13
14
Qcso
Old colluvium and sheetwash deposits, undivided
Old colluvium and sheetwash deposits, undivided
Qcso
Qcso
DMUUnit1
02-03-06
Upper Pleistocene
Old colluvium and sheetwash deposits, undivided (Upper Pleistocene) — Unit Qcso occurs on the western side of the Coalbank Creek valley in the north part of the quadrangle. Unlike unit Qcs, it does not form distinct fans and aprons. The unit was delineated based on its smoother surface observed in lidar imagery, in contrast to the surrounding bedrock, which has a more irregular surface.
The unit consist of sheetwash deposits that are light brownish gray to very pale brown, moderately to poorly sorted, silty clay or clayey silty sand. The sand ranges from very fine to coarse, with minor gravel up to 1 cm in size. Larger gravel is scattered throughout the unit, ranging from granules to 20 cm boulders, with an average size around 6 cm. The unit exhibits Stage I carbonate development, with scattered calcic carbonate filaments, clasts with <1 mm thick rinds, and strong effervescence.
Bedrock residuum (unit Kfh) was observed from an animal burrow, suggesting that the unit most likely has residuum at a shallow depth. CaCO3 cemented sandstone boulders (from unit Kfh) were also observed in the ravine near the center of the unit. Unit Qcso may include reworked eolian sediment. The thickness is estimated to be 1 to 2 m, although the exact thickness of unit Qcso is not known, as no water wells are located in its vicinity. Areas mapped as unit Qcso are locally susceptible to small debris flows and swelling or collapsing soils. This unit may serve as a local source of sand.
Alluvial sediment, mostly coarse-grained
Medium
234-200-144
None
DAS1
DMU14
15
Qu
Quaternary undivided
Quaternary undivided
Qu
Qu
DMUUnit1
02-03-07
Holocene to Pleistocene
Quaternary undivided (Holocene to Pleistocene) — Shown in cross section only. Alluvium and eolian deposits of the Severance quadrangle undivided. This unit locally may contain residuum from underlying bedrock (Robson and others, 2000a and b).
Alluvial sediment, mostly coarse-grained
High
255-255-102
None
DAS1
DMU15
16
None
BEDROCK GEOLOGY HEADER
BEDROCK GEOLOGY
BEDROCK GEOLOGY
None
DMUHeading1
03
None
None
None
None
None
None
DAS1
DMU16
17
PENbh
Conglomeratic Sandstone of Black Hollow Reservoir
Conglomeratic Sandstone of Black Hollow Reservoir
PENbh
PENbh
DMUUnit1
03-01
Upper Cretaceous (Paleogene?)
Conglomeratic Sandstone of Black Hollow Reservoir (Upper Cretaceous (Paleogene?)) — The unit is comprised of very pale brown (10 YR) and pale yellow (2.5Y), poorly sorted conglomeritic sandstone with a matrix dominated by coarse- to very coarse-grained sand with minor very fine- to medium-grained sand. Sand grains are mostly rounded to well-rounded with about 75% quartz, 24% feldspar and other minerals, and 1% opaque minerals. Gravel clasts are predominantly subrounded to well-rounded and range in size from granule to 3 cm diameter pebbles with rare cobbles up to 11 cm in diameter. Clasts are primarily potassium feldspar granitic rocks, dark, fine-grained metamorphic rocks, and iron concretions. The unit is moderately to strongly indurated with a CaCO3 cement with strong to violent effervescence. The unit is cross-bedded to massive; cross-beds range from a scale of centimeter to tens of centimeters. Unit PENbh was only mapped along the eastern shore of the Black Hollow Reservoir where it is underlain by unit Kp. Unlike the surrounding Cretaceous units, it does not dip to the east at about 4°.
The exposure at Black Hollow Reservoir is approximately 1 m-thick and 17 m-long. Due to its small area, unit PENbh is represented as a point on Plate 1. At the unit’s contact with the underlying unit Kp, a meter thick PENbh layer was precipitated from groundwater flow. Although not in-situ, boulders possibly equivalent to this unit were observed about 230 m to the east of the Black Hollow outcrop and another boulder was observed in a ravine within unit Qcso about 3 km to the east. A detrital zircon sample (SV085CDZ, see Table 3) from the Black Hollow outcrop yielded a youngest age population of 71.3 ± 1.5 Ma (number of concordant analyses [n]=6; mean-square weighted deviation [MSWD] =0.77; youngest single grain of 67.8 ± 2.9 Ma). In the Milliken quadrangle (35 km south of Black Hollow Reservoir), a lithologically similar unit was mapped mantling at Wildcat Mound. Detrital zircons collected from this site (n = 58) yielded an age estimate of 28 Ma (Palkovic and others, 2018). Another lithologically similar unit was mapped and dated in the south-central part of the Timnath quadrangle (12 km southwest of Black Hollow Reservoir) where a detrital zircon age (n = 102) yielded an age estimate of 27.5 ± 1.4 Ma (Perman and others, 2025). While the ages at the Timnath and Milliken quadrangles may correlate to the Ogallala Formation (possibly began accumulating in the Oligocene or early Miocene) at its western extent (Smith and others, 2016; Morgan and others, 2023; Morgan and O’Keeffe, 2023; Kainz and others, 2023); the age at Black Hollow Reservoir is about twice as old (youngest date 67.8 ± 2.9 Ma). Based on the absence of ~28 Ma zircons, it is possible that unit PENbh has an age that is pre-Ogallala and may be similar to the Arikaree Formation, White River Formation, or older. Although very unlikely, it is important to point out the possibility that the analytical results from this study could be accurate, which would suggest unit PENbh may be Cretaceous in age. According to Raynold (2022), the age of the Arapahoe Conglomerate, part of the Denver Formation D1 Sequence found mainly in the Denver area, has an age estimate around 67 Ma. The Denver Formation D1 Sequence was deposited during the Laramide Orogeny uplift of the Rocky Mountains when precipitation was high, resulting in the formation of large fan deposits (Leier and others, 2005) and river systems that generally flowed north from the Denver area (Dechesne and others, 2011). It is possible that unit PENbh may have been deposited during this period.
Sandstone
High
158-87-50
None
DAS1
DMU17
18
Kl
Laramie Formation
Laramie Formation
Kl
Kl
DMUUnit1
03-02
Upper Cretaceous
Laramie Formation (Upper Cretaceous) — The unit is comprised of light- to dark-gray, interbedded siltstone, silty sandstone, and carbonaceous shale. The lower portion of the unit consists of light- to medium-gray, quartzose sandstone beds that are separated by shale beds and coal seams. The upper portion consists of claystone, shale, sandy shale, lignite, and lenticular sandstone beds.
In a few areas in the quadrangle as well as throughout the Colorado Piedmont, the contact between units Kl and Kfh is difficult to distinguish due to its gradational and shingled stratigraphy (Odouli, 1966; Briscoe, 1972; Dechesne and others, 2011). In the Severance quadrangle, the contact between units Kl and Kfh is from Shelton and Rogers (1975) which was modified from previous work (Mather and others, 1928; Briscoe 1972; Hershey and Schneider 1972). While unit Kl can be identified easily in boreholes by its coal layers to the east, the contact between it and unit Kfh is difficult to define due to the gradational contact and being mostly mantled by soil and Quaternary deposits. Hershey and Schneider (1972) interpreted the contact to be about one km east of the WCR 25 and 86 junction while Shelton and Roger (1975) say the contact in the eastern edge of the Coalbank Creek valley.
North of the Greeley Arch (see Geologic History and Structure), the total thickness of the Laramie Formation is about 488-545 m (Weimer, 1977; Kirkham and Lagwig, 1980). However, water well logs in Cross Section A indicate the unit is about 46-61 m thick in the Severance quadrangle. These measurements concur with those of Shelton and Rogers (1975).
Sandstone and mudstone
High
168-230-138
None
DAS1
DMU18
19
Kfh
Fox Hills Sandstone
Fox Hills Sandstone
Kfh
Kfh
DMUUnit1
03-03
Upper Cretaceous
Fox Hills Sandstone (Upper Cretaceous) — The unit is comprised of white, pale yellow, pale brown (5Y and 2.5Y), very fine- to fine-grained sandstone with minor silt. The sandstone is friable, breaking along bedding planes, weakly to moderately indurated, and predominantly massive but has some weak bedding and crossbedding ranging from 1-10 cm thick. Iron oxide staining is locally present along bedding planes. The unit generally does not have any CaCO3 minerals and does not effervesce but carbonate fillings are present in the fractures and veinlets as thick as 5 mm. Orphiomorpha burrows, petrified wood, shell fossil fragments, and local millimeter scale rip up mud clasts are present in the unit. Locally, unit Kfh is comprised of indurated, very fine- to fine-grained sandstone. In the Bracewell quadrangle, this facies consists of highly resistant, dark brown to dark gray, fine-grained sandstone cemented by silica and crops out in oblong lenticular bodies (Palkovic, 2020). This indurated sandstone may be locally cemented by CaCO3.
While most of the unit is covered by Quaternary sediments and soil throughout the quadrangle, it is exposed in the Coalbank Creek valley in the northern part of the quadrangle and dips to the east at 4°. The contact of unit Kfh with the underlying unit Kp and overlying unit Kl is gradational. Like the contact between units Kfh and Kl, historically, the contact between the upper part of unit Kp (also known as the Pierre Transition Member) and unit Kfh was difficult to define. According to Lovering and others (1932), the contact was defined by being 75 m below unit Kl, and Scott and Cobban (1965) stated that the contact was unmappable. In the Bracewell quadrangle, the author included the Transition Member within the Fox Hills Formation due to the difficulty of delineating the contact (Palkovic, 2020). Like units Kl and Kfh, the contact in this map between units Kp and Kfh was defined using the contact from Shelton and Rogers (1975) (see unit Kl).
Two detrital zircon samples were collected from near the upper portion of unit Kfh, near the Kfh/Kl contact: one along WCR 86 (SV003DZ, see Table 3), which yielded a youngest age population of 74.9 ± 1.7 Ma (n = 3; MSWD = 0.56; youngest single grain of 70.8 ± 4.3 Ma), and one along WCR 25 (SV051DZ, see Table 3), which yielded a youngest age population of 67.6 ± 2.1 Ma (n = 5; MSWD = 0.62; youngest single grain of 63.7 ± 3.5 Ma). Additionally, another detrital zircon sample (SV021DZ, see Table 3) was collected near the base of unit Kfh from a site near the center of the quadrangle, by WCR 80, near the Kfh/Kp contact. This sample yielded a youngest age population of 73.3 ± 1.6 Ma (n = 13; MSWD = 0.93; youngest single grain of 69.4 ± 3.4 Ma). The 74.9 ± 1.7 Ma and 73.3 ± 1.6 Ma dates are within the ages of the Fox Hills Sandstones at Limon, Colorado, which yielded a youngest age population of 76.6 ± 1.2 Ma (youngest single grain of 74 ± 2 Ma) and 72.2 ± 1.0 Ma (youngest single grain of 67 ± 3 Ma) (Morgan and others, 2023; Morgan and O’Keeffe, 2023).
Water well logs from CO DWR (2023) in Cross Section A indicate that the unit is up to 33 m-thick, while Shelton and Rogers (1975) report that the unit is up to 18 m-thick, and Workman and others (2018) estimate the unit to be up to 24 m-thick.
Sandstone
High
235-255-204
None
DAS1
DMU19
20
Kp
Pierre Shale
Pierre Shale
Kp
Kp
DMUUnit1
03-04
Upper Cretaceous
Pierre Shale (Upper Cretaceous) — The unit is comprised mainly of medium- to dark-gray shale with an upward gradation to siltstone and silty sandstone that make up the upper Pierre Shale Transition Zone Member (Shelton and Rogers, 1975). The unit is mostly covered by Quaternary sediment and soil, but it is exposed on the bluffs on the eastern shores of Black Hollow Reservoir where it is overlain by units Qe, Qg1, and PENbh. At this location, unit Kp is comprised of alternating dark grayish-brown to olive gray (5Y and 2.5Y) shale and pale brown to light yellowish-brown (2.5Y) siltstone and fine-grained sandstone layers. Bedding ranges from planar lamination to wavy beds up to 1 cm thick. The unit is friable and breaks into platy and blocky fragments. Some of the sandy beds are discontinuous. While the shaley beds have no CaCO3; the sandy beds effervesce and have 1-2 mm carbonate veinlets. Locally, iron oxide coatings are present. At Black Hollow Reservoir, this unit dips at 4° east. Spheroidal concretions as large as 60 cm in diameter were observed and are common in the upper Pierre Transition Zone Member (Scott and Cobban, 1965). In addition, indurated portions of the shale have cone-in-cone structures about 5 cm-thick. The unit also has sandy gypsum lenses about 3-6 cm-thick with yellow to orange, very fine- to medium-grained sand and smaller white lenses of fine sand about 1 mm thick. Gypsum crystals are present and form 1 mm to 3 cm thick plates and weather to an acicular habit. “Swallowtail” twins and gypsum “flowers” are also present. Indurated, pale brown, carbonate cemented, fine- to medium-grained sandstone beds locally contain burrows and fossil shells as long as 5 cm. Fragments of these indurated sandstones were observed in the overlaying eolian deposits throughout the western portion of the quadrangle. Unit Kp was also observed in an irrigation ditch along WCR 21 where it is mostly thin, gray shale beds interlayered with indurated, fine-grained, discontinuous sandstone beds. Total unit thickness is approximately 2,055-2,208 m.
Mudstone
High
137-137-68
None
DAS1
DMU20
21
Kn
Niobrara Formation
Niobrara Formation
Kn
Kn
DMUUnit1
03-05
Upper Cretaceous
Niobrara Formation (Upper Cretaceous) — Shown in cross section only. Very fissile, dark gray shale with thin layers of micritic limestone. Important source of oil and gas in the Denver Basin. Total thickness is approximately 76-100 m.
Mudstone
High
235-255-178
None
DAS1
DMU21
22
Kcgg
Colorado Group
Colorado Group
Kcgg
Kcgg
DMUUnit1
03-06
Upper Cretaceous
Colorado Group (Upper Cretaceous) — Shown in cross section only. Units comprising the group include the Codell Sandstone, Carlile Shale (near-shore sandstone and shale), Graneros Shale (shale with interbedded sandstone), and Greenhorn Limestone (shale, limestone, and chalky shale). Two wells penetrate the underlying Dakota Group: 05-123-23201 and 05-123-26741. Based on those wells, unit Kcgg combined approximately thickness is about 140-142 m.
Mostly mudstone
High
204-255-48
None
DAS1
DMU22
23
Bedrock
Bedrock undivided
Bedrock undivided
Bedrock
Bedrock
DMUUnit1
03-07
Paleogene to upper Cretaceous
None
Sandstone and mudstone
High
189-170-138
None
DAS1
DMU23
24
Water
Water
Water
Water
Water
DMUHeading1
04
Holocene
None
Water or ice
High
151-219-242
None
DAS1
DMU24
Glossary
OBJECTID
Term
Definition
DefinitionSourceID
Glossary_ID
35
1SD
A statistic used as a measure of the dispersion or variation in a distribution or set of data, equal to the square root of the arithmetic mean of the squares of the deviations from the arithmetic mean.
DICT1
GLO01
34
95%
95 Percent of 100
DICT1
GLO02
37
95.5%
95 and a half percent of 100
DICT1
GLO33
21
anticline, concealed
A fold, generally convex upward, whose core contains the stratigraphically older rocks.
GEODICT1
GLO04
15
borehole, geotechnical
A circular hole made by drilling; esp. a deep hole of small diameter, such as an oil well or a water well.
GEODICT1
GLO05
10
borehole, oil & gas
A circular hole made by drilling; esp. a deep hole of small diameter, such as an oil well or a water well.
GEODICT1
GLO06
6
borehole, water
A circular hole made by drilling; esp. a deep hole of small diameter, such as an oil well or a water well.
GEODICT1
GLO07
3
boundary
A line along which two areas meet; a line of demarcation between contiguous political or geographic entities.
GEODICT1
GLO08
12
C14
Carbon-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues to date archaeological, geological and hydrogeological samples
GEODICT1
GLO09
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
GLO10
8
contact
A plane or irregular surface between two types or ages of rock; examples are faults, intrusive borders, bedding planes separating distinct strata, and unconformities; approximately located.
GEODICT1
GLO11
9
contact, approximate
A plane or irregular surface between two types or ages of rock; examples are faults, intrusive borders, bedding planes separating distinct strata, and unconformities.
GEODICT1
GLO12
24
contact, concealed
A plane or irregular surface between two types or ages of rock; examples are faults, intrusive borders, bedding planes separating distinct strata, and unconformities.
GEODICT1
GLO13
4
cross section
A diagram or drawing that shows features transected by a given plane; specif. a vertical section drawn at right angles to the longer axis of a geologic feature.
GEODICT1
GLO14
30
DMUHeading1
GeMS hierarchy formatting term
GEMS1
GLO15
28
DMUHeading2
GeMS hierarchy formatting term
GEMS1
GLO16
27
DMUUnit1
GeMS hierarchy formatting term
GEMS1
GLO17
31
Dome
An uplift or anticlinal structure, either circular or elliptical in outline, in which the rocks dip gently away in all directions.
GEODICT1
GLO18
23
dome, concealed
An uplift or anticlinal structure, either circular or elliptical in outline, in which the rocks dip gently away in all directions.
GEODICT1
GLO19
13
DZ
A scientific technique for understanding the age and provenance of sedimentary deposits. To determine the age of zircons deposited within a specific sedimentary unit, mass spectrometry is used to measure the abundance of radioisotopes in the grains, most commonly the uranium–lead ratio. Zircon is a common accessory or trace mineral constituent of most granite and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircons contain trace amounts of uranium and thorium and can be dated using several modern analytical techniques.
DICT2
GLO20
29
High
unusual or considerable in degree, power, intensity, etc.
DICT1
GLO21
26
Medium
Something that is intermediate in amount, size, or quality.
DICT1
GLO22
19
oblique-slip, right lateral fault
A strike-slip fault on which the side opposite the observer has been displaced to the right; the net slip has dip slip and strike slip components.
GEODICT1
GLO23
14
OSL
Optically-Stimulated Luminescence is a late Quaternary dating technique used to date the last time quartz sediment was exposed to light. As sediment is transported by wind, water, or ice, it is exposed to sunlight and zeroed of any previous luminescence signal.
GEODICT1
GLO24
25
paleovalley
Low-lying land bordered by higher ground; esp. an elongate, relatively large, gently sloping depression of the Earth's surface, commonly situated between two mountains or between ranges of hills or mountains, and often containing a stream with an outlet. It is usually developed by stream erosion, but may be formed by faulting; prehistoric.
GEODICT1
GLO25
11
physiographic feature, water
A prominent or conspicuous physiographic form or noticeable part thereof.
GEODICT1
GLO26
32
radiocarbon BP
The conventional radiocarbon age in years BP (before present) reflects the concentration of radiocarbon in a sample (with 0 BP defined as the radiocarbon concentration in AD 1950).
GEODICT1
GLO27
22
syncline, concealed
A fold of which the core contains the stratigraphically younger rocks; it is generally concave upward.
GEODICT1
GLO28
20
thrust fault
A fault with a dip of 45° or less over much of its extent, on which the hanging wall has moved upward relative to the footwall.
GEODICT1
GLO29
17
tickmark, vertical
Used in diagrams or graphs to indicate points or increments of measurement along a line.
DICT2
GLO30
18
wireframe
A visual representation of a website or app's structure and layout, showing where content, navigation, and functional elements will be placed, but without any graphic design, color, or text.
DICT1
GLO31
33
year
The time taken by the earth to make one revolution around the sun.
DICT1
GLO32
MiscellaneousMapInformation
OBJECTID
MapProperty
MapPropertyValue
MiscellaneousMapInformation_ID
1
ACKNOWLEDGMENTS
The authors would like to thank the following for their assistance with this investigation. Ralph Shroba (Colorado Geological Survey geologist and U.S. Geological Survey Scientist Emeritus) was a peer reviewer and provided constructive comments and information to the authors. Dr. Steven L. Forman of Baylor University, Waco, Texas performed the optically stimulated luminescence (OSL) analyses. Beta Analytics, Inc. Miami, Florida performed radiocarbon analyses. Dr. Mark Schmitz of Boise State University performed the detrital zircon analyses and provided the concordant analyses of the data. Michael O’Keeffe (Colorado Geological Survey) provided helpful discussions about the mineral resources within the Severance area. Jonathan White (Colorado Geological Survey Emeritus) provided valuable information and suggestions for the map. Joanna Redwine (Colorado Geological Survey STATEMAP Program Manager) and Matthew Morgan (State Geologist and Colorado Geological Survey Director) reviewed the final product and provided valuable feedback. Caitlin Bernier and David “Barney” Barnett of Pangaea Geospatial, in Gunnison, Colorado, produced the final map plates and GIS files. Benjamin Tescher and Rachel Turner from the Colorado State Land Board permitted the authors to do fieldwork within the property owned by the Land Board. Nicolas Wharton and Lindsey Radcliffe-Coombes (Town of Severance) also permitted the authors to do fieldwork within the municipality of Severance. Finally, the authors would also like to thank Ryan Woodland of Woodland Home Marketplace, and other landowners in the Severance Reservoir quadrangle who permitted the authors to visit and work on their properties.
MMI01
2
AUTHORS
By Alexander E. Marr, Emily A. Perman, and Kassandra O. Lindsey
2025
MMI02
3
GEOLOGIC HISTORY
The Severance quadrangle is located about 100 km northeast of Denver and within the Front Range Urban Corridor. The quadrangle lies within the northern part of the Colorado Piedmont, a physiographic province bounded by the Rocky Mountains to the west and High Plains to the north and east (Fenneman, 1931; Leonard, 2002; Smith and others, 2016). Fluvial erosion and geomorphic evolution of the ancestral South Platte River and its tributaries during the Pliocene have removed most of the Paleogene and Neogene rocks in the northern Colorado Piedmont (Madole, 1991). The result is a scoured region that is topographically lower than the surrounding physiographic provinces. The elevation range within the Severance quadrangle is about 1447-1615 m (4749-5297 ft) with a total relief of 167 m (548 ft). South of the quadrangle, incision along the Cache la Poudre River and its three tributaries: The Slough, Coalbank Creek valleys, and the “Eaton” paleovalley (named coined from Robson and others (2000a)) contribute to the relatively low relief in the area. These three tributaries were possibly part of an ancient tributary system to the Cache al Poudre River that flowed roughly north to south in the quadrangle. These streams had a higher competence and formed wide stream valleys. Over time, the stream competence decreased, resulting in large paleovalleys with low flowing underfit streams (Robson and others, 2000a).
The Severance quadrangle lies along the western part of the Greeley Arch, a structural saddle that separates the Cheyenne Basin to the north and Denver Basin to the south (Dechesne and others, 2011). The Denver Basin is an asymmetrical, oval-shaped, structural basin extending as far east as southwest Nebraska and southeast Wyoming to the north reaching of Pueblo, Colorado (Tweto, 1975). Though none are present at the ground surface in the mapped area, the oldest bedrock units underlying the Denver Basin are Pennsylvanian in age (300 million years ago) and were deposited during the uplift of the Ancestral Rocky Mountains. The three oldest units mapped in this quadrangle were deposited when the Western Interior Seaway covered the Denver Basin area 100-60 million years ago). During this time, the Pierre Shale (unit Kp) was deposited in an offshore marine environment. The Western Interior Seaway began regressing to the east when the Laramide Orogeny initiated the modern Rocky Mountain uplift about 70 million years ago. Sediments deposited in regressing seas and near-shore environments now comprise of the Fox Hills Sandstone (unit Kfh) and Laramie Formation (unit Kl). Most of the bedrock dips gently to the east at around 4°.
Compression during the Laramide Orogeny formed the Windsor Wrench fault zone and associated small synclines and anticlines (Stone, 1969; Stone, 1985; Weimer, 1996). The anticlines trapped valuable oil resources (Stone, 1985; Weimer, 1996; Higely and Cox, 2007). The Windsor Wrench fault zone is a right-lateral, oblique-slip fault zone that strikes from the city of Boulder northeastward, through the Severance quadrangle, and continues northeastward towards Briggsdale (about 36 km east of the quadrangle). Although the fault zone and oil fields are not shown in Cross Section A, around the Windsor Wrench fault zone are three oil fields that extracted oil from the Permian Lyons Sandstone in the Severance quadrangle: New Windsor, Black Hollow, and Pierce. These oil fields were developed within small anticlines in Paleozoic rocks (Higely and Cox, 2007). The Black Hollow oil field developed in the north central portion of the quadrangle. Faults within the Pierce and Black Hollow fields have minor vertical separation about less than 30 m (Stone, 1985). Structural elements on this map are taken from Weimer (1996) who used subsurface data for those interpretations. Cross Section A crosses two synclines, which were previously mapped by Weimer (1996). The east-vergent, westernmost fold is asymmetrical and more easily recognized than the broad easternmost fold.
During the Paleogene and Neogene, sediment eroded from the uplifting Rocky Mountains was deposited to the east, within the newly formed Denver Basin lowland. By the Lower-Middle Pliocene, the dominating processes switched from aggradation to erosion owing to increased precipitation and broad uplifts in the Rocky Mountains (Duller and others, 2012; Marder and others, 2023). Erosion mostly removed the Paleogene and Neogene rocks in the western portion of the Denver Basin, leaving only Cretaceous rocks exposed; however, there are isolated outcrops of Cenozoic units preserved throughout the Colorado Piedmont.
The “Conglomeratic Sandstone of Black Hollow Reservoir” is the youngest mapped bedrock unit in the Severance quadrangle (unit PENbh). This unit is exposed on the eastern shores of Black Hollow Reservoir. Initially, this unit was correlated to a similar looking units nearby in the Timnath and Milliken quadrangles 12 and 35 km away, respectfully (Palkovic and others, 2018; Perman and others, 2025). These correlations were based on similar lithology and very limited extent of the unit. However, results from detrital zircon analyses suggest unit PENbh may be significantly older than expected and therefore may not correlate to units in nearby quads as initially interpreted. Alternatively, additional analyses may be needed to confirm the accuracy of the detrital zircon results to represent the age of deposition of unit PENbh. Considering this unexpected result, several possible regional correlations are presented below.
For the Timnath and Milliken sites, their detrital zircon ages came back to 27.5 ± 1.4 Ma and 28 Ma, respectively. Based on the age results from the Timnath and Milliken quadrangles, it is possible that these relic Cenozoic units may have been correlative or deposited co-valley with the Ogallala Formation (the Ogallala possibly began accumulating in the Oligocene or early Miocene) at its western extent (Smith and others, 2016; Morgan and others, 2023; Morgan and O’Keeffe, 2023; Kainz and others, 2023). However, detrital zircon results at Black Hollow Reservoir suggest that unit PENbh may be significantly older: the unit yielded a youngest age population of 71.3 ± 1.5 Ma (number of concordant analyses [n]=6; mean-square weighted deviation [MSWD] =0.77; youngest single grain of 67.8 ± 2.9 Ma). Since unit PENbh at Black Hollow Reservoir does not have any zircons younger than 28 Ma, it is possible that this unit may be older than the Ogallala Formation and may have an age similar to the Arikaree Formation, White River Formation, or older. A second possibility, although perhaps more questionable, is that unit PENbh is not correlative to other similar units mapped in this region but was deposited by north trending river systems during the uplift of the Rocky Mountains around 67 ka, similar to depositional systems described by Dechesne and others (2011).
Surficial deposits mantle most of the bedrock throughout the quadrangle. Since the beginning of the Pleistocene, the Colorado Piedmont has undergone cyclic geomorphic responses to glacial and interglacial climatic conditions. The geomorphic response is alternating episodes of erosional scouring and aggradation of relatively coarse-grained sediments throughout the Colorado Piedmont (Bryan and Ray, 1940; Hunt, 1954; Scott, 1963). The surficial deposits mapped in the Severance quadrangle are Holocene and Upper Pleistocene eolian silt/clay and sand (unit Qe), alluvium and mass wasting (units Qa, Qcs, Qcso), and older Middle Pleistocene gravel deposits (units Qg2, Qg1 and Qg).
Units Qg2, Qg1 and Qg are coarse-grained, fluvial gravel units that were deposited by eastward flowing, high-energy streams during late glacial and/or interglacial periods during the Middle Pleistocene. These units are mapped mainly in the highlands between The Slough and Coalbank Creek valleys in the northwest portion of the quadrangle and also make up the alluvium deposited within the “Eaton” paleovalley on the eastern side of the quadrangle.
Unit Qg2 forms high ridges in the northern part of the quadrangle and is generally poorly preserved, has Stage III-IV carbonate development, and has been extensively mantled by eolian deposits. This unit may be correlative with the Verdos Alluvium. Based on elevation (60 to 75 m) above modern streams (i.e. Cache la Poudre River), Colton (1978) mapped areas that were mapped as unit Qg2 as Verdos Alluvium within the Severance quadrangle. The upper, middle, and local base of the Verdos Alluvium has been reported to have deposits of Lava Creek B ash, which erupted from the Yellowstone Caldera, and deposited and preserved in multiple locations in the Denver area (Kellogg and others, 2008). While the age of the Lava Creek B tephra is ~631 ka (Matthews and others, 2015), the uppermost, younger deposits of the Verdos Alluvium are estimated to be about 410-475 ka based on correlation with MIS stage 14 age estimates from the marine oxygen isotope curve (Kellogg and others, 2008).
Near Black Hollow Reservoir a gravel deposit (unit Qg1) was observed with Stage I-II carbonate development and a 10 cm thick Bt soil horizon. Three samples were collected for age dating using optical stimulated luminescence (OSL) (see Table 2). While the results are inconclusive, the oldest sample collected at Black Hollow Reservoir yielded a date of 304 ka, but is an infinite result, the second oldest sample had a date of 73,810 ± 7,820 SAR OSL years, and the third sample came back to 7,685 ± 210 SAR OSL years. Other unit Qg1 numerical ages in the surrounding area are estimated to be about 133 ka in the Timnath quadrangle (Perman and others, 2025) and 341 ka in the Valley View School quadrangle (Keller and Marr, 2023). Unit Qg1 may also be correlative to the Slocum Alluvium which has been dated to 300-220 ka in the Denver Area (Kellogg and others, 2008). Based on the carbonate development, it is likely that the 7,685 ± 210 years estimate may be too young. Although the 73,810 ± 7,820 estimate at Black Hollow Reservoir is younger, the 304 ka age, despite being infinite, is similar to the age estimate at Valley View School quadrangle and upper estimate of the Slocum Alluvium. Owing to its gravelly, coarse-grained texture, units Qg1 and Qg2 are less susceptible to erosion compared to the underlying Cretaceous units in the mapped area, which leads to the inverted topography with unit Qg2 mantling many of the uplands in the mapped area.
Since the Middle Pleistocene, the Cache la Poudre River has been flowing near its modern course (Workman and others, 2018). At one point, the valleys of The Slough, Coalbank Creek, and the “Eaton” paleovalley used to have higher discharge and sediment load as seen by the large valleys with small ephemeral streams and thick sand and gravel deposits in The Slough and “Eaton” paleovalley (see Cross Section B). Since the Holocene, streams in The Slough and Coalbank Creek valleys, and small streams above the “Eaton” paleovalley have been depositing alluvium (unit Qa). A radiocarbon age for a sample (SV018C14, see Table 1) taken from alluvium in a cut bank along The Slough, south of the town of Severance, yielded an age of 1,170 ± 30 calibrated years before present (cal. yrs BP). Around the same time, colluvium and sheetwash deposits (unit Qcs and Qcso) were being deposited on the valley margins of The Slough and Coalbank Creek.
Eolian deposits (unit Qe) is the dominant map unit of the Severance quadrangle. The sediment sources of these types of deposits come from the alluvium in major stream valleys (i.e. Cache la Poudre), and local bedrock units (Muhs and others, 1996; Muhs and others, 1999). The age of this unit is Upper Pleistocene to Holocene and broadly covers much of the Colorado Piedmont and eastern plains. In the Severance quadrangle, two C14 dates (SV019CC14 and SV032C14, see Table 1) collected from unit Qe yielded age estimates of 8,770 ± 30 and 7,440 ± 30 years BP. The Upper Pleistocene-aged deposits are generally more extensive due to deposition from northwest winds during the Pinedale glaciation (Madole and others, 2005). On the eastern shores of Black Hollow Reservoir, unit Qe filled in clastic dikes or ice wedges in the underlying Pierre Shale. The formation of these structures may be related to periglacial processes. Two OSL samples were collected at the Black Hollow Reservoir site: one from within a sand wedge (SV086AOSL, see Table 2) and one from the overlying, undisrupted sand unit (SV086OSL, see Table 2). The OSL analyses of the overlying sand unit yielded an age of 13,860 ± 645 SAR-OSL years and the sand wedge of 13,755 ± 685 SAR-OSL years.
MMI03
4
MINERAL RESOURCES
The Severance quadrangle is located in the western part of the Denver Basin and Weld County. The quadrangle contains the following mineral resources: oil and gas, coal, uranium, and sand and gravel. The Severance quadrangle lies in the northwest margin of the Wattenberg oil field which is a productive oil and gas field that is mostly in Weld and Adam Counties. The Wattenberg Field is the fourth largest oil field in the United States and ninth largest gas field based on proved reserves (EIA, 2021). According to O’Keeffe (2025), Weld County has an estimated total production value of over $12 billion in oil and gas production and produced over 133 million oil barrels in 2023. Oil and gas infrastructure is dominant in the central and southern portions of the quadrangle. The Niobrara Formation (unit Kn) is the principal production horizon in the Wattenberg Field. Other formations with production horizons include the Shannon/Hygiene Sandstone (middle member of the Pierre Shale (unit Kp)), the Codell Sandstone (upper part of the Colorado Group (unit Kcgg)), the J sandstone (from the Muddy Formation), and the D sandstone of the Dakota Group (Fishman, 2005). Three small oilfields that produced oil primarily from the Permian Lyons Sandstone are located within and around the Severance quadrangle: New Windsor, Black Hollow, and Pierce. In these oilfields, oil is trapped by a combination of oil-producing bedrock units and small anticlines (Clark and Rold, 1961; Higley and Cox, 2007). Oil and natural gas cumulative production from these fields were 10.8 million barrels and 0.330 million cubic feet of gas in Black Hollow and 11.5 million barrels in Pierce (Higely and Cox, 2007). Cretaceous formations also serve as important source rocks for oil in these fields: the Black Hollow field produces oil from the Niobrara Formation (unit Kn) and Codell Sandstone (unit Kcgg); the New Windsor field produced oil from the Terry, Hygiene/Shannon members of unit Kp, and Codell Sandstone (unit Kcgg) (Higely and Cox, 2007).
The Laramie Formation (unit Kl), which underlies the central and eastern portion of the quadrangle, is an important coal source in the Denver Basin. The quality of coal in the Laramie Formation ranges from lignite to subbituminous (Cappa and TerBest, 2002). Coal from the Laramie Formation north of Greeley was limited because the coal deposits are relatively thin and discontinuous (Kirkham and Ladwig, 1979; Roberts, 2007). The average received heat of combustion from the coal mined north of Greeley ranges from 7,200 to 8,000 British Thermal Unit (BTU)/lb (Kirkham, 1978; Kirkham and Ladwig, 1979). There are no historical coal mines reported in the Severance quadrangle; however, Shelton and Rogers (1975) stated that the eastern part of the quadrangle has limited potential for coal development. Coal productive areas continue to the east of the mapped area.
Units Qa, Qg2, Qcs, and Qcso are potential sources of local sand and gravel. There are no active industrial gravel quarries in the Severance quadrangle. A single historic quarry is shown in Coalbank Creek excavated into unit Qcs (1960 USGS topographic map and Schwochow and others, 1974). Due to the high content of both fines and calcium carbonate present in units Qg2, Qcs, Qcso, the deposits are not considered suitable sources for concrete aggregate and may only be suitable for fill material Schwochow and others (1974).
Uranium was discovered in Weld County in 1969, primarily in the Fox Hill Sandstone and Laramie Formation (units Kfh and Kl, respectively) (Reade, 1978). Most of the historical uranium mining occurred in the Grover and the Briggsdale areas, located about 89 km to the northeast of the Severance quadrangle. In the past, the uranium ore was low grade (varies from 150,000 to 1,000,000 lbs U3O8) and were commercially significant in the 1970s because of high demand from the nuclear industry (Reade, 1978). There are no active or historic uranium mines in the Severance quadrangle, although areas with potential for yielding uranium are present (Shelton and Rogers, 1975). North of the Severance quadrangle is a proposed exploration project called the Centennial Project with conceptual designs to extract in-situ uranium. The original owner of the project, Powertech (USA) Inc., controlled about 9,615 acres of fee mineral ownership and 7,262 acres of surface ownership (SRK Consulting, 2010). The project extends from the Colorado/Wyoming border (about 42 km) to the northern boundary of the Severance quadrangle. In the project area, the uranium ore occurs in the Fox Hills Sandstone (unit Kfh) as rolling front deposits in the form of small pods to elongated lobes. Ore mineralogy is mainly uraninite, coffinite, and carnotite with some vanadium (SRK Consulting, 2010). As of 2023, enCore Energy Corp. owns the Centennial Project and there is no update on production within the project area ( https://miningdataonline.com/property/1230/profile.aspx?pid=1230 ).
The Laramie-Fox Hills aquifer is a bedrock aquifer in the Denver Basin. It consists of two relatively thick sandstone units in the basal portion of the Laramie Formation (unit Kl) and the underlying Fox Hills Sandstone (unit Kfh) (Topper and others, 2003). The aquifer is as much as 107 m thick, but the water pumped zones are rarely thicker than approximately 60 m and is generally under artesian pressure (Topper and others, 2003). The aquifer exists primarily in the eastern part of the Severance quadrangle. Unit Kl is absent in the central section of the quadrangle and both units Kl and Kfh are absent in the western part. While the Pierre Shale (unit Kp) is generally a confining layer, the upper sandy transition member can yield small quantities of groundwater (Hershey and Schneider, 1964; Briscoe, 1972). This part of the Pierre Shale has historically been known as the “Upper Pierre Aquifer” (Kirkham and others, 1980). Sand and gravel deposits in units Qg2, Qg, Qa, Qcs, and sand-rich Qe may be local groundwater sources. According to CO DWR (2023), the maximum well depth in the Severance quadrangle is 259 m (850 ft) and the average well production is about 93 liters per minute (24.5 gallons per minute).
The Pierre Shale and Laramie Formation (units Kp and Kl, respectively) are known to contain swelling clays that can impact building and infrastructure if not properly treated and mitigated (Hart, 1974). Surficial units derived from these formations, such as units Qa, Qe, Qcs, and Qcso, may also produce hazards related to swelling soils. In addition to swelling, these units may also be hydrocompactive (collapsible) (White and Greenman, 2008). When these types of soil are dry, the finer-sized particles (clay and silt) act as binding agents which increases the compressive strength of the soil. When soil is wet, fine particles can be packed into a denser configuration such that void space in the soil is decreased. This compaction can cause settlement at the ground surface with resultant damage to structures (White and Greenman, 2008).
Units Qcs and Qcso may be susceptible to debris flows where they occur on valley slopes within The Slough and Coalbank Creek.
In the Severance quadrangle, areas underlain by unit Qa may be prone to flooding, especially within the bottom of The Slough, Coalbank Creek, and the western portion of the “Eaton” paleovalley. According to the Federal Emergency Management Agency (FEMA), these valleys are designated as 100 year floodplains (FEMA, 2023).
In June 2014, an earthquake near Greeley was caused by an apparent oil wastewater injection with a moment-magnitude (Mw) of 3.2 and Modified Mercalli intensity of IV. This earthquake was strong enough to be felt throughout the Front Range (Yeck and others, 2016). From 1960 to 2023, there was only one recorded earthquake around the Severance quadrangle area with a magnitude of 2.6 in 2016 south of the town of Eaton (USGS Online Earthquake Catalogue, 2023).
MMI04
5
REFERENCES
Baylor University, 2025, What is OSL dating?: Baylor University Department of Geosciences website: https://geosciences.artsandsciences.baylor.edu/about-us/facilities/geoluminescence-dating-research-lab/what-osl-dating , accessed March, 2025
MMI05
6
REFERENCES
Briscoe, H.J., Jr., 1972, Stratigraphy and aquifer characteristics of the Fox Hills sandstone in the Greeley area, Weld County, Colorado: M.S. thesis, Colorado School of Mines, 78 p.
MMI06
7
REFERENCES
Bryan, K., and Ray, L.L., 1940, Geologic antiquity of Lindenmeier site in Colorado: Smithsonian Miscellaneous Collections., v. 99, p. 65-86.
MMI07
8
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/ ]
MMI08
9
REFERENCES
Clark, R.W., and Rold, L., 1961, New Windsor field, Weld County, Colorado, p. 202–205, in Parker, J.M., ed., Colorado-Nebraska oil and gas fields: Rocky Mountain Association of Geologists.
MMI09
10
REFERENCES
CO DWR (Colorado Division of Water Resources), 2023, Driller’s logs incorporated with water-well permits [Available at https://dwr.colorado.gov/services/data-information/gis ]
MMI10
11
REFERENCES
CO ECMN (Colorado Energy and Carbon Management Commission), 2023, Colorado Oil and Gas Commission data download: Colorado Oil and Gas Commission, monthly production by county [ Available at https://ecmc.state.co.us/data4.html#/production ]
MMI11
12
REFERENCES
Colton, R.B., 1978, Geologic map of the Boulder-Fort Collins-Greely area, Front Range Urban Corridor, Colorado: U.S. Geological Survey Miscellaneous Investigation Map I-855-G, scale 1:100,000 [ Available at https://pubs.usgs.gov/imap/855/G/ ]
MMI12
13
REFERENCES
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 ]
MMI13
14
REFERENCES
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
15
REFERENCES
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.
MMI15
16
REFERENCES
EIA (Energy Information Administration), 2021, Colorado state profile and energy estimates: U.S. Energy Information Administration [Available at https://www.eia.gov/state/?sid=CO ].
MMI16
17
REFERENCES
Federal Emergency Management Agency (FEMA), 2023, FEMA's National Flood Hazard Layer (NFHL) Viewer [available at https://hazards-fema.maps.arcgis.com/apps/webappviewer/index.html?id=8b0adb51996444d4879338b5529aa9cd ].
MMI17
18
REFERENCES
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.
MMI18
19
REFERENCES
Fenneman, N.M., 1931, Physiography of western United States: New York, McGraw-Hill Book Co, 534 p.
MMI19
20
REFERENCES
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/ ]
MMI20
21
REFERENCES
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.
MMI21
22
REFERENCES
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
23
REFERENCES
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.
MMI23
24
REFERENCES
Hart, S.S., 1974, Potential swelling soil and rock in the Front Range Urban Corridor, Colorado: Colorado Geological Survey Environmental Geology 7 [Available at https://coloradogeologicalsurvey.org/publications/potentially-swelling-soil-rock-front-range-urban-corridor-colorado/ ].
MMI24
25
REFERENCES
Hershey, L.A., and Schneider, P.A., Jr., 1964, Ground-Water investigations in the lower Cache la Poudre River Basin, Colorado: US Geological Survey Water-Supply Paper 1669-X, 22 p. [ Available at https://pubs.usgs.gov/publication/wsp1669X ].
MMI25
26
REFERENCES
Hershey, L.A., and Schneider, P.A., Jr., 1972, Geologic map of the lower Cache la Poudre River basin, northcentral Colorado: U.S. Geological Survey Miscellaneous Geological Investigation Map I-687, scale 1:62,500 [Available at https://pubs.usgs.gov/publication/i687 ].
MMI26
27
REFERENCES
Higley, D.K., and Cox, D.O., 2007, Oil and gas exploration and development along the Front Range in the Denver Basin of Colorado, Nebraska, and Wyoming in Petroleum systems and assessment of undiscovered oil and gas in the Denver Basin Province, Colorado, Kansas, Nebraska, South Dakota, and Wyoming: U.S. Geological Survey, Digital Data Series, DDS-69-P., 45 p. [Available at https://pubs.usgs.gov/pp/2005/1698/508/chapB.html ].
MMI27
28
REFERENCES
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].
MMI28
29
REFERENCES
International Union of Geological Sciences, 2023, International Commission on Stratigraphy, version 2023/09 [Available at https://stratigraphy.org/chart#latest-version ].
MMI29
30
REFERENCES
Kainz, S.J., Abbott, L.D., Flowers, R.M., Olsson, A., Fernandez, S., and Metcalf, J.R., 2023, Cenozoic exhumation across the High Plains of Southeastern Colorado from (U-Th)/He Thermochronology: Lithosphere, v. 2023_310, 26 p.
MMI30
31
REFERENCES
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/ ].
MMI31
32
REFERENCES
Keller, S.M., and Marr, A.E., 2024, Geologic map of the Windsor quadrangle, Larimer and Weld Counties, Colorado: Colorado Geological Survey Open File Report 22-05, scale 1:24,00 [Available at https://ngmdb.usgs.gov/Prodesc/proddesc_116252.htm ].
MMI32
33
REFERENCES
Keller, S.M., and Morgan, M.L., 2020, Geologic map of the Greeley quadrangle, Weld County, Colorado: Colorado Geological Survey Open-File Report 20-05, scale 1:24,000 [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-greeley-quadrangle-weld-colorado/ ].
MMI33
34
REFERENCES
Kellogg, K.S., Shroba, R.R., Bruce, B., and Premo, W.R., 2008, Geologic map of the Denver West 30' x 60' quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3000, scale 1:100,000 [Available in https://pubs.usgs.gov/sim/3000/ ].
MMI34
35
REFERENCES
Kirkham, R.M., 1978, Coal mines and coal analyses of the Denver and Cheyenne Basins, Colorado: Colorado Geological Survey Open-File Report 78–9, 104 p. [Available in https://coloradogeologicalsurvey.org/publications/coal-mines-coal-analysis-denver-cheyenne-basins-colorado/ ].
MMI35
36
REFERENCES
Kirkham, R.M., and Ladwig, L.R., 1979, Coal resources of the Denver and Cheyenne Basins, Colorado: Colorado Geological Survey Resource Series 5, 76 p. [Available in https://coloradogeologicalsurvey.org/publications/coal-resources-denver-cheyenne-basins-colorado/ ].
MMI36
37
REFERENCES
Kirkham, R.M., and Ladwig, L.R., 1980, Energy resources of the Denver and Cheyenne Basins, Colorado—Resource characteristics, development potential, and environmental problems: Colorado Geological Survey Environmental Geology 12, 258 p. [Available in https://coloradogeologicalsurvey.org/publications/energy-resources-denver-cheyenne-basin-colorado-characteristics-development-environmental/ ].
MMI37
38
REFERENCES
Kirkham, R.M., O’Leary, W., and Warner, J.W., 1980, Hydrogeologic and stratigraphic data pertinent to uranium mining, Cheyenne Basin, Colorado: Colorado Geological Survey Information Series 12, 31 p. [Available in https://coloradogeologicalsurvey.org/publications/hydrogeologic-stratigraphic-data-uranium-mining-cheyenne-basin-colorado/ ].
MMI38
39
REFERENCES
Leier, A.L., DeCelles, P.G., and Pelletier, J.D., 2005, Mountains, monsoons, and megafans: Geology, v. 33, p. 289–292.
MMI39
40
REFERENCES
Leonard, E.M., 2002, Geomorphic and tectonic forcing of the Cenozoic warping of the Colorado Piedmont: Geology, v. 30, no. 7, p. 595-598.
MMI40
41
REFERENCES
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.
MMI41
42
REFERENCES
Lovering, T.S., Aurand, H.A., Lavington, C.S., and Wilson, J.H., 1932, Fox Hills Formation, northeastern Colorado: American Association of Petroleum Geologists Bulletin, v. 16, no. 7, p. 702-703.
MMI42
43
REFERENCES
Machette, M.N., 1985, Calcic soils of the southwestern United States, p. 1-21, 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, 150 p.
MMI43
44
REFERENCES
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.
MMI44
45
REFERENCES
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.usgs.gov/sim/2005/2875/ ].
MMI45
46
REFERENCES
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.
MMI46
47
REFERENCES
Mather, F.K., Gilluly, J., and Lusk, R.G., 1928, Contributions to economic geology (short papers and preliminary reports), 1927, Part II, Mineral fuels. Geology and oil and gas prospects of northeastern Colorado: U.S. Geological Survey Bulletin, 796-B, 124 p. [Available at https://pubs.usgs.gov/publication/b796B ].
MMI47
48
REFERENCES
Matthews, N. E., Vazquez, J. A., and Calvert, A. T., 2015, Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals: Geochem. Geophys. Geosyst., v. 16, p. 2508–2528.
MMI48
49
REFERENCES
McComas, M. R., 1966, Environmental control of inorganic water quality near Severance, Colorado: M.S. thesis, Colorado State University, 52 p.
MMI49
50
REFERENCES
Mears, B., Jr., 1981, Periglacial wedges and the late Pleistocene environment of Wyoming's intermontane basins: Quaternary Research, v. 15 (2), p. 171-198.
MMI50
51
REFERENCES
Morgan, M.L., and O’Keefe, M.K., 2023, Data tables of detrital zircon U-Pb geochronologic analyses and trace element concentrations of select Cretaceous, Paleogene, and Neogene rocks, Denver Basin and Northeastern Colorado (Data) – v20231110: Colorado Geological Survey ON-004-04D – V20231110 [Available at https://coloradogeologicalsurvey.org/publications/front-range-detrital-zircon/ ].
MMI51
52
REFERENCES
Morgan, M.L., O’Keefe, M.K., Mahatma, A.A., and Keller, S.M., 2023, Detrital zircon age estimates of select Upper Cretaceous and Neogene sedimentary rocks, Denver Basin and northeastern, Colorado: Geological Society of America Abstracts with Programs, v. 55, no. 5.
MMI52
53
REFERENCES
Muhs, D.R., Aleinikoff, J.N., Stafford, T. W., Jr., Been, Josh, Mahan, S.A., and Cowherd, Scott, 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.
MMI53
54
REFERENCES
Muhs, D.R., Cattle, S.R., Crouvi, O., Rosseau, D.D., Sun, J., and Zarate, M.A., 2014, Loess records, p. 411-441, in Knippertz, P., Stuut, J.B.W., eds., Mineral Dust. Springer Netherlands, Dordrecht, 509 p.
MMI54
55
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Muhs, D.R., Stafford, T.W., Cowherd, S.D., Mahan, S.A., Kihl, R., Maat, P.B., Bush, C.A., Nehring, J., 1996, Origin of the late Quaternary dune fields of northeastern Colorado: Geomorphology, v. 7, p. 129-149.
MMI55
56
REFERENCES
Munsell Color, 1991, Munsell soil color charts, 1990 edition revised: Newburgh, NY, Macbeth Division of Kollmorgan Instruments Corp.
MMI56
57
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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.
MMI57
58
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Nichols, G., 2009, Sedimentology and stratigraphy (second edition): Wiley-Blackwell, Chichester (United Kingdom), 419 p.
MMI58
59
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Nissen, T.C., 1985, Field and laboratory studies of selected periglacial wedge-polygons in Southern Wyoming: M.S. thesis, University of Wyoming, 175 p.
MMI59
60
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Noe, D.C., 2010, Anton escarpment paleoseismologic investigation, Washington County, Colorado: Colorado Geological Survey unpublished Hazard, National Earthquake Hazards Reduction Program (NEHRP) Program FY-2007, External Grant Award Number 07HQGR0090.
MMI60
61
REFERENCES
O’Keeffe, M.K., 2025, Colorado mineral and industry activities 2023-2024: Colorado Geological Survey Information Series 87 [Also available at https://coloradogeologicalsurvey.org/publications/colorado-mineral-energy-industry-activities-2024/ ].
MMI61
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REFERENCES
Odouli, K., 1966, Geology of northeastern Larimer and northwestern Weld Counties, Colorado: M.S. thesis, Colorado School of Mines, 146 p.
MMI62
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REFERENCES
Palkovic, M.J., 2020, Geologic map of the Bracewell quadrangle, Weld County, Colorado: Colorado Geological Survey Open-File Report 20-03, scale 1:24,000 [Available at https://coloradogeologicalsurvey.org/publications/geologic-map-bracewell-quadrangle-weld-colorado/ ].
MMI63
64
REFERENCES
Palkovic, M.J., Lindsey, K.L., and Morgan, M.L., 2018, Geologic map of the Milliken quadrangle, Weld County: Colorado Geological Survey Open File Report 18-02, scale 1:24,000 [Available in https://coloradogeologicalsurvey.org/publications/geologic-map-milliken-quadrangle-weld-colorado/ ].
MMI64
65
REFERENCES
Perman, E.A., Lindsey, K.L., and Marr, A.E., 2025, Geologic map of the Timnath quadrangle, Larimer and Weld Counties, Colorado: Colorado Geological Survey Open File Report 24-02 scale 1:24,00.
MMI65
66
REFERENCES
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.
MMI66
67
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Ramsey, C.B., 2009, Bayesian analysis of radiocarbon dates: Radiocarbon, v. 51, p. 337-360.
MMI67
68
REFERENCES
Raynolds, R.G., Cretaceous stratigraphy of Colorado: Colorado Geological Survey Map Series 54 [Available from at https://coloradogeologicalsurvey.org/publications/cretaceous-stratigraphy-colorado ].
MMI68
69
REFERENCES
Reade, H.L., 1978, Uranium deposits: Northeastern Denver Julesburg Basin, Colorado: Rocky Mountain Association of Geologists – 1978 Symposium, p. 161-171.
MMI69
70
REFERENCES
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.
MMI70
71
REFERENCES
Roberts, S.B., 2007, Coal in the Front Range Urban Corridor – An overview of coal geology, coal production, and coalbed methane potential in selected areas of the Denver Basin, Colorado and the potential effects of historical coal mining on development and land-use planning: Chap. 3 in Higely, D.K., ed., Petroleum systems and assessment of undiscovered oil and gas in the Denver Basin Province, Colorado, Kansas, Nebraska, South Dakota, and Wyoming, U.S. Geological Survey Digital Data Series DDS–69–P, 49 p. [Available in https://pubs.usgs.gov/pp/2005/1698/508/chapF.html#heading157747304 ].
MMI71
72
REFERENCES
Robson, S.G., Arnold, L.R., and Heiny, J.S., 2000a, Geohydrology of the shallow aquifers in the Greeley-Nunn area, Colorado: U.S. Geological Survey Hydrologic Atlas 746-A [Available at https://pubs.usgs.gov/publication/ha746A ].
MMI72
73
REFERENCES
Robson, S.G., Arnold, L.R., and Heiny, J.S., 2000b, Geohydrology of the shallow aquifers in the Fort Collins-Loveland area, Colorado: U.S. Geological Survey Hydrologic Atlas 746-B [Available at https://pubs.usgs.gov/publication/ha746B ].
MMI73
74
REFERENCES
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/ ].
MMI74
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REFERENCES
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].
MMI75
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REFERENCES
Scott, G.R., and Cobban, W.A., 1965, Geologic and biostratigraphic map of the Pierre Shale between Jarre Creek and Loveland, Colorado: U.S. Geological Survey Miscellaneous Geological Investigation Maps I-439, scale 1:48,000 [Available at https://pubs.usgs.gov/publication/i439 ].
MMI76
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REFERENCES
Shelton, D.C., and Rogers, W.P., 1975, Environmental and engineering geology of the Windsor study area, Larimer and Weld Counties, Colorado: Colorado Geological Survey Engineer Geology 6, Maps A-K, scale 1:48,000 [Available at https://coloradogeologicalsurvey.org/publications/environmental-engineering-geology-windsor-larimer-weld-colorado/].
MMI77
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REFERENCES
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, p. 93-124, in Keller, S.M., and Morgan, M.L., eds., Unfolding the geology of the West; Geological Society of America Field Guide 44, 419 p.
SRK Consulting Engineers and Scientists, 2010, NI 43-101 preliminary assessment Powertech Uranium Corp. Centennial Uranium Project Weld County, Colorado: SRK Project Number: 194300.020.
MMI80
81
REFERENCES
Stone, D.S., 1969, Wrench faulting and Rocky Mountain tectonics: The Mountain Geologist, v. 6, no. 2, p. 67-7.
MMI81
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REFERENCES
Stone, D.S., 1985, Seismic profiles in the area of the Pierce and Black Hollow fields, Weld County, Colorado, in Gries, R.R., and Dyer, R.C., eds., Seismic exploration of the Rocky Mountain Region: Rocky Mountain Association of Geologists and Denver Geophysical Society, p. 79–86.
MMI82
83
REFERENCES
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 ].
MMI83
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REFERENCES
Tweto, O., 1975, Laramide (Late Cretaceous-Early Tertiary) Orogeny in the Southern Rocky Mountains, p. 1-44, in Curtis, B.F. ed., Cenozoic History of the Southern Rocky Mountains: Geological Society of America Memoir 144, 279 p.
MMI84
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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. [Available at https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_053572 ].
Weimer, R.J., 1977, Stratigraphy and tectonics of western coals, p. 9–27, in Murray, D.K., ed., Geology of Rocky Mountain coal: Colorado Geological Survey Resource Series 1, 175 p [Available in https://coloradogeologicalsurvey.org/publications/geology-rocky-mountain-coal-symposium-1976/ ].
MMI87
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REFERENCES
Weimer, R.J., 1996, Guide to the petroleum geology and Laramide orogeny, Denver Basin and Front Range, Colorado: Colorado Geological Survey, Bulletin 51, 133 p. [Available at https://coloradogeologicalsurvey.org/publications/denver-basin-front-range-colorado-petroleum-geology-laramide-orogeny/ ].
MMI88
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REFERENCES
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/ ].
MMI89
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REFERENCES
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, n. 4, p. 369-391.
MMI90
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REFERENCES
Workman, J.B., Cole, J.C., Shroba, R.R., Kellogg, K.S., and Premo, W.R., 2018, Geologic map of the Fort Collins 30’x60’ quadrangle, Larimer and Jackson Counties, Colorado, and Albany and Laramie Counties, Wyoming: U.S. Geological Survey Scientific Investigation Maps 3399, scale 1:100,000 [Available in https://pubs.usgs.gov/publication/sim3399 ].
MMI91
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REFERENCES
Yeck, W.L., Benza, H.M., Weingarten, M., and Nakai, J., 2016, Rapid response, monitoring, and mitigation of induced seismicity near Greeley, Colorado: Seismological Research Letters, v. 87, n. 4, p. 837-847.
MMI92
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STATEMAP AGREEMENT
This mapping project was funded jointly by the Colorado Geological Survey and the U.S. Geological Survey
through the National Cooperative Geologic Mapping Program under STATEMAP agreement G23AC00403-00.
Although assigned an OFR number in 2024, this report was published in 2025.
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TITLE
GEOLOGIC MAP OF THE SEVERANCE QUADRANGLE, WELD COUNTY, COLORADO
MMI94
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.