| 2.1 Has required elements: nonspatial tables DataSources, DescriptionOfMapUnits, GeoMaterialDict; feature dataset GeologicMap with feature classes ContactsAndFaults and MapUnitPolys | PASS |
| 2.2 Required fields within required elements are present and correctly defined | PASS |
| 2.3 All MapUnitPolys and ContactsAndFaults based feature classes obey Level 2 topology rules: no internal gaps or overlaps in MapUnitPolys, boundaries of MapUnitPolys are covered by ContactsAndFaults | PASS |
| 2.4 All map units in MapUnitPolys have entries in DescriptionOfMapUnits table | PASS |
| 2.5 No duplicate MapUnit values in DescriptionOfMapUnit table | PASS |
| 2.6 Certain field values within required elements have entries in Glossary table | PASS |
| 2.7 No duplicate Term values in Glossary table | PASS |
| 2.8 All xxxSourceID values in required elements have entries in DataSources table | PASS |
| 2.9 No duplicate DataSources_ID values in DataSources table | PASS |
| 3.1 Table and field definitions beyond Level 2 conform to GeMS schema | PASS |
| 3.2 All MapUnitPolys and ContactsAndFaults based feature classes obey Level 3 topology rules: No ContactsAndFaults overlaps, self-overlaps, or self-intersections. | PASS |
| 3.3 No missing required values | PASS |
| 3.4 No missing terms in Glossary | PASS |
| 3.5 No unnecessary terms in Glossary | PASS |
| 3.6 No missing sources in DataSources | PASS |
| 3.7 No unnecessary sources in DataSources | PASS |
| 3.8 No map units without entries in DescriptionOfMapUnits | PASS |
| 3.9 No unnecessary map units in DescriptionOfMapUnits | PASS |
| 3.10 HierarchyKey values in DescriptionOfMapUnits are unique and well formed | PASS |
| 3.11 All values of GeoMaterial are defined in GeoMaterialDict. GeoMaterialDict is as specified in the GeMS standard | PASS |
| 3.12 No duplicate _ID values | PASS |
| 3.13 No zero-length, whitespace-only, or bad null values | PASS |
| MapUnit | DescriptionOfMapUnits | CrossSectionC | CrossSectionA | CrossSectionB | GeologicMap | CorrelationOfMapUnits |
|---|---|---|---|---|---|---|
| Qafo | X | -- | X | X | X | X |
| Qa1 | X | -- | -- | -- | X | X |
| Qaf | X | -- | -- | -- | X | X |
| Qa2 | X | -- | -- | -- | X | X |
| Kpl | X | X | -- | -- | X | X |
| Qa2/Qa3 | X | -- | X | X | -- | -- |
| af | X | -- | X | X | X | X |
| PPsif | X | X | -- | -- | -- | X |
| Kp | X | -- | X | X | -- | -- |
| Qa3 | X | -- | -- | -- | X | X |
| TRPly | X | X | -- | -- | -- | X |
| Kpm | X | -- | -- | -- | X | X |
| water | X | -- | -- | -- | X | -- |
| JTRmj | X | X | -- | -- | -- | X |
| no data | X | X | -- | -- | -- | -- |
| Qa4 | X | -- | -- | X | X | X |
| Kn | X | X | -- | -- | X | X |
| Kplr | X | -- | -- | -- | X | X |
| Kpmu | X | X | -- | -- | -- | X |
| Kph | X | X | -- | -- | X | X |
| Kcgg | X | X | -- | -- | -- | X |
| Kpu | X | -- | -- | -- | X | X |
| Qe | X | -- | -- | X | X | X |
| Kd | X | X | -- | -- | -- | X |
| Qa | X | -- | X | X | X | X |
| OBJECTID | Source | Notes | URL | DataSources_ID |
|---|---|---|---|---|
| 8 | American Geosciences Institute Glossary | Glossary | https://glossary.americangeosciences.org/ | AGI |
| 4 | Baylor University | Geoluminescence Dating Research Lab | https://geosciences.artsandsciences.baylor.edu/about-us/facilities/geoluminescence-dating-research-lab | BAYLOR |
| 2 | This study | this study | None | DAS1 |
| 9 | Online dictionary | None | https://www.merriam-webster.com/dictionary/geotechnical | DICT1 |
| 6 | Colorado Division of Water Resources | None | https://dwr.colorado.gov/ | DWR |
| 5 | Colorado Energy and Carbon Management Commission | None | https://ecmc.state.co.us/#/home | ECMC |
| 7 | City of Fort Collins | Geotechnical soil boring | None | FCGEOTECH |
| 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 |
| 10 | GeMS standard | None | https://ecmc.state.co.us/#/home | GeMS1 |
| 3 | Colorado Geological Survey Land Use Review | Geotechnical soil boring | None | LUR |
| OBJECTID | MapUnit | Name | FullName | Age | Description | HierarchyKey | ParagraphStyle | Label | Symbol | AreaFillRGB | AreaFillPatternDescription | DescriptionSourceID | GeoMaterial | GeoMaterialConfidence | DescriptionOfMapUnits_ID |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 30 | None | DESCRIPTION OF MAP UNITS | DESCRIPTION OF MAP UNITS | None | Notes on frequently used references and terminology: All reported optically stimulated luminescence (OSL) analysis data are in Table 1 on Plate 2. All colors are from hand samples unless otherwise stated. Website links for the Federal Emergency Management Agency (FEMA) flood mapping, Colorado Division of Water Resources (DWR), and Colorado Energy and Carbon Management Commission (ECMC) are in the reference section. The Cache la Poudre River is referred to as the Poudre River hereafter. | 00 | DMUHeading1 | None | None | None | None | DAS1 | None | None | DMU01 |
| 1 | None | SURFICIAL UNITS | SURFICIAL UNITS | None | None | 01 | DMUHeading1 | None | None | None | None | DAS1 | None | None | DMU02 |
| 2 | None | HUMAN-MADE DEPOSITS | HUMAN-MADE DEPOSITS | None | None | 01-01 | DMUHeading2 | None | None | None | None | DAS1 | None | None | DMU03 |
| 3 | af | Artificial fill | Artificial fill | uppermost Holocene | The unit consists of clay, silt, sand, gravel, and cobbles deposited as fill or rip-rap. Fill and rip-rap are placed to support roadways and highways, mitigate damage to buildings from natural geologic hazards like expansive soils, construct earthen dams, and during land reclamation practices after the completion of quarrying operations. Much of the area underlain by unit af in the quadrangle is disturbed and reworked areas from active or reclaimed gravel quarries. Artificial fill likely exists below and around human-made structures, even though it may not be mapped in the quadrangle. A good example of this is the eastern edge of Warren Lake Reservoir; houses are constructed on damming material up to the eastern edge of the reservoir, but because there are structures built here, unit af is not mapped. If not placed and compacted properly, areas underlain by unit af may experience hazards related to expansive soils, soil collapse, erosion, and (or) slope failure, especially in areas where the Pierre Shale members are near the surface. Thickness varies but is likely at least 2 m thick below buildings and local roadways and may be as much as 6 m below highways. | 01-01-01 | DMUUnit1 | af | af | 255-255-255 | None | DAS1 | "Made" or human-engineered land | High | DMU04 |
| 4 | None | ALLUVIAL DEPOSITS | ALLUVIAL DEPOSITS | None | None | 01-02 | DMUHeading2 | None | None | None | None | DAS1 | None | None | DMU05 |
| 6 | Qa1 | Alluvium one | Alluvium one | Upper Holocene | The unit is comprised of poorly to moderately sorted, massive, clay, silt, and sand, and clast-supported gravel deposited by the Poudre River. Exposures are poor in the mapped area; in general, deposits are typically light brown to dark brown in color. The unit is most commonly exposed in gravelly and sandy bars present along reaches of the Poudre River that are not modified by quarrying operations. Deposits underlie the modern river and low-lying terraces that are 2 m (or less) above the modern channel. Post-Piney Creek Alluvium was previously mapped underlying the whole modern Poudre River channel (Colton, 1978; Kellogg and others, 2008; Cole and Braddock, 2009; Workman and others, 2018). Most areas underlain by the unit have a 1% annual chance of flooding (Zone AE), and some have a 0.2% annual chance as mapped by FEMA; therefore, these areas may be prone to flooding, erosion, and (or) sediment inundation. The unit is not a likely source of sand or gravel. The unit may be as much as 2 m thick. | 01-02-01 | DMUUnit1 | Qa1 | Qa1 | 255-255-190 | 130-130-130 602-gravel | DAS1 | Alluvial sediment, mostly fine-grained | Medium | DMU06 |
| 7 | Qa2 | Alluvium two | Alluvium two | Middle to Lower (?) Holocene | The unit is chiefly comprised of poorly to moderately sorted, massive clay, silt, sand, and clast-supported gravel. Sandy deposits are mostly homogeneous and massive. Discontinuous pebble lenses that are as much as 2.5 cm thick are present locally. Clasts in gravelly deposits are 3 to 5 cm in diameter, in a sandy matrix. The unit is light brown, reddish-brown, or dark brown in color. Many areas underlain by unit Qa2 have been heavily modified by quarrying activities to access the underlying gravel deposits of unit Qa3. Unit Qa2 underlies low-lying terraces as high as 3 m above the Poudre River. A quarry in NW ¼, sec. 33, T. 7 N., R. 68 W. exposes units Qa2 and Qa3. The area is mapped as af because its surface has been heavily reworked, deposits are in the process of being removed, and the area will continue to be modified until it has been reclaimed. In 2023, four OSL samples were collected from in-situ deposits exposed in active quarry walls. Two samples are discussed here, and the others are discussed with unit Qa3 below. Sample FC-SCQ-23-02 was collected from a silty sand Qa2 deposit, approximately 0.6 m below ground surface (bgs). The sample yielded a SAR-OSL age estimate of 6,100 ± 210 yrs. Sample FC-SCQ-23-03 was collected from a sandy lens in a clast-supported gravel deposit, approximately 1.9 m bgs. This sample yielded a SAR-OSL age estimate of 5,085 ± 325 yrs. See the Geologic History on Plate 2 for more discussion. The unit may be a potential source of sand or gravel, though it is typically removed to access the underlying gravelly deposits of unit Qa3. Areas underlain by unit Qa2 may be prone to flooding, erosion, and (or) sediment inundation, especially areas directly adjacent to the Poudre River. Deposits are typically around 2 m thick but may be as much as 4 m thick locally. | 01-02-02 | DMUUnit1 | Qa2 | Qa2 | 254-246-136 | 215-176-158 random dot fill | DAS1 | Alluvial sediment, mostly fine-grained | High | DMU07 |
| 5 | Qa | Alluvium | Alluvium | Upper to Lower (?) Holocene | The unit is comprised chiefly of light brown to brown clay, silt, and sand. Discontinuous gravel lenses may be present locally. The unit is mapped in the valleys of ephemeral drainages, which have incised into unit Qafo. Deposits of Qa are of similar age to units Qa1 and Qa2, but are not geomorphologically differentiable, such as units Qa1 and Qa2. Post-Piney Creek Alluvium has previously been mapped underlying many of these ephemeral drainages (Colton, 1978; Kellogg and others, 2008; Cole and Braddock, 2009; Workman and others, 2018). Areas underlain by the unit may be prone to flooding, sediment inundation, and (or) erosion. Deposits of Qa are not likely sources of sand or gravel. The unit is typically around 2 m thick but may be as much as 5 m thick locally. | 01-02-03 | DMUUnit1 | Qa | Qa | 255-255-175 | None | DAS1 | Alluvial sediment, mostly fine-grained | High | DMU08 |
| 8 | Qa3 | Alluvium three | Alluvium three | Lower Holocene to Upper Pleistocene | Unit Qa3 deposits underlie unit Qa2 along much of the modern Poudre River. Where exposed at the ground surface, unit Qa3 underlies terraces 3 to 8 m above the modern river channel. Unit Qa3 is well exposed in a quarry in NW ¼, sec. 33, T. 7 N., R. 68 W. The area is mapped as unit af because its surface has been heavily reworked, deposits are in the process of being removed, and the area will continue to be modified until it has been reclaimed. Here, the unit is tan, gray, and brown in color. Clast-supported cobble-gravel comprises most of the unit and is interlayered with matrix-supported gravel, sand beds, and pebble-gravel beds. Coarser gravelly alluvium is poorly sorted. Clasts are typically as much as 20 cm in diameter, but may be larger locally, and are subround to round. Clasts are derived from Precambrian bedrock west of the mapped area, with minor sedimentary clasts sourced closer to the mapped area. Pebble-gravel and sand beds are typically as much as 8 cm thick and laterally continuous over several meters. Pebble-gravel beds are moderately to poorly sorted, comprised chiefly of medium to coarse sand and pebbles, and are massive. Sand beds are moderately sorted, contain fine- to coarse-grained sand, generally lack pebbles, and are either planar- or cross-bedded. Iron-oxide and manganese staining are prevalent throughout the deposit. Two samples were collected from the exposure at the quarry located in the NW ¼, sec. 33, T. 7 N., R. 68 W., and analyzed using OSL techniques. In 2023, samples FC-SCQ-23-01 (0.8 m bgs) and FC-SCQ-23-04 (4.3 m bgs) were collected from in-situ alluvium exposed in quarry walls. These samples yielded SAR-OSL age estimates of 9,665 ± 415 yrs and 16,025 ± 975 yrs, respectively. These samples and deposits are discussed in more detail in the Geologic History on Plate 2. Unit Qa3 has previously been mapped as Broadway Alluvium, which is roughly correlative with the later part of the Pinedale glaciation (Colton, 1978; Kellogg and others, 2008; Cole and Braddock, 2009; Workman and others, 2018). The Pinedale glaciation ended by 12 ka while outwash continued until around 10 ka (Holliday, 1987). The unit is a source of gravel. Perched groundwater may be present at the base of the unit where it overlies clayey and shaley members of the Pierre Shale (unit Kp). Where unit Qe overlies unit Qa3 deposits, soils may be prone to collapse. The unit may be as much as 10 m thick locally. | 01-02-04 | DMUUnit1 | Qa3 | Qa3 | 254-246-136 | 85-255-0 random dot fill | DAS1 | Alluvial sediment | High | DMU09 |
| 31 | Qa4 | Alluvium four | Alluvium four | Upper Pleistocene to upper Middle (?) Pleistocene | A cutbank in NW ¼, sec. 18, T. 7 N., R. 68 W. exposes 1 m of clast-supported gravel underlying 2 m of sandy alluvium. The deposit is reddish-brown in color. The upper sandy alluvium is comprised chiefly of silt to coarse sand and is massive. Secondary carbonate to a maximum of Stage II is present, indicating the unit is at least late Middle to early Late Pleistocene in age (Machette, 1985; Birkeland, 1999). Gravel clasts in a silt- to sand-matrix comprise the lower part of the deposit and lie beneath the developed soil. Clasts lack carbonate rinds at this location. Clasts are generally up to 15 cm in diameter, but are larger locally, and are typically subround. A weak fining-upward sequence may be present at the contact between the upper sandy alluvium and the underlying gravel; pea-sized gravel and coarse sand are abundant at the contact. The 3 m of alluvium overlies the Pierre Shale (unit Kp), which is exposed at this site. This Qa4 deposit underlies an exposed terrace approximately 9 to 11 m above the modern Poudre River. In other locations, this unit likely underlies higher terraces that are completely mantled by unit Qe. Sample FC-KF-23-01 was collected 2 m bgs, near the contact of the upper fines and lower gravel, and was analyzed using TT-OSL (Thermally Transferred Optically Stimulated Luminescence) techniques. It yielded a SAR-OSL age estimate of 76,820 ± 5,210 yrs and is correlative with marine isotope stage (MIS) 4-5 (Lisiecki and Raymo, 2005). This sample predates the Pinedale glaciation (ended by 12 ka; Madole and Shroba, 1979) and post-dates the Bull Lake glaciation (ended by 120 ka; Madole, 1991). Unit Qa4 is correlative with the Louviers Alluvium of Colton (1978), Kellogg and others (2008), Cole and Braddock (2009), and Workman and others (2018). Kellogg and others (2008) included MIS 5-aged deposits (70-130 ka; Lisiecki and Raymo, 2005) and MIS 6-aged deposits (130-190 ka; Lisiecki and Raymo, 2005) as Louviers Alluvium. The deposit at and near this site has previously been mapped as the Broadway Alluvium (Colton, 1978; Kellogg and others, 2008; Cole and Braddock, 2009; Workman and others, 2018). See the Geologic History on Plate 2 for more discussion. The unit may be a source of sand and (or) gravel. Though none are mapped, localized slope failures may initiate at or near the contact of the unit with the underlying bedrock, especially where the underlying bedrock is relatively weak, like unit Kp. Perched groundwater may be present at the base of the unit where it overlies clayey and shaley members of the Pierre Shale (unit Kp). The unit is as much as 6 m thick, according to DWR well logs. | 01-02-05 | DMUUnit1 | None | None | None | None | DAS1 | Alluvial sediment | High | DMU10 |
| 34 | Qa2/Qa3 | Alluvium two/Alluvium three | Alluvium two/Alluvium three | Middle Holocene to Upper Pleistocene | Shown in cross section only (Plate 2). | 01-02-06 | DMUUnit1 | Qa2/Qa3 | Qa2/Qa3 | 254-246-136 | 215-176-158 & 85-255-0 random dot fill | DAS1 | Alluvial sediment, mostly fine-grained | High | DMU11 |
| 9 | None | ALLUVIUM AND MASS-WASTING DEPOSITS | ALLUVIUM AND MASS-WASTING DEPOSITS | None | None | 01-03 | DMUHeading2 | None | None | None | None | DAS1 | None | None | DMU12 |
| 11 | Qaf | Debris-flow and alluvial-fan deposits | Debris-flow and alluvial-fan deposits | Holocene | There are no outcrops of the unit in the mapped area; however, distinct, fan-shaped landforms are mapped as unit Qaf on the south side of the Poudre River escarpment. As the river incised, it exposed unit Qafo and the underlying members of the Pierre Shale. Subsequently formed ephemeral drainages have incised into unit Qafo during episodic above-average precipitation and runoff, and deposited alluvial-fan and debris-flow deposits at their outlets in the modern Poudre River valley. Colluvium may also be present locally. Debris-flow deposits are typically poorly sorted, matrix-supported gravel or poorly sorted mud, sand, and clay. Alluvial-fan deposits are typically poorly sorted and may contain clay to gravel. Alluvium is typically moderately to well sorted and may be stratified or massive. Colluvium is typically poorly sorted and may be difficult to distinguish between debris flow and alluvial-fan deposits. Areas underlain by the unit may be subject to future debris flow or alluvial-fan processes and (or) flooding. The unit is not a likely source of sand or gravel. Deposits may be as much as 3 m thick, but may be thicker locally. | 01-03-01 | DMUUnit1 | Qaf | Qaf | 255-255-190 | 115-178-255 602-gravel | DAS1 | Debris flows, landslides, and other localized mass-movement sediment | High | DMU13 |
| 12 | Qafo | Old debris-flow and alluvial-fan deposits | Old debris-flow and alluvial-fan deposits | Middle Pleistocene | The unit is not well exposed in the quadrangle, but many DWR logs and geotechnical borings record and describe the deposits. The unit is typically light brown, brown, reddish-brown, or olive-brown in color and is calcareous locally. Deposits are typically either silty clay and clayey silt or consist of sand and gravel. Much of unit Qafo deposits are mantled by unit Qe; however, given the limited exposure and lack of distinguishing morphology in well and geotechnical logs, Qe is mapped with unit Qafo in most of the quadrangle. The unit underlies surfaces at several distinct levels, indicating episodic deposition punctuated by periods of incision, especially by the ancestral Fossil Creek in the southern part of the mapped area, during the Middle Pleistocene (Section A-A’ and Section B-B’, Plate 2). The unit has previously been mapped as Slocum Alluvium (Colton, 1978; Kellogg and others, 2008; Cole and Braddock, 2009; Workman and others, 2018). Deposits underlying the fan-shaped surface in the southwest corner of the quadrangle are either thin (less than 1 m) or have been completely eroded near the apex of the landform. Similar deposits were evaluated in trenches on the Larimer County Landfill property in the Loveland Quadrangle (Lindsey, 2024). Here, no true fluvial gravel deposits were identified. Instead, the deposits were poorly sorted, calcareous, and comprised of clay, sand, and pebble-gravel, interpreted as alluvial fans. Two samples were collected from two trench sites and analyzed using infrared stimulated luminescence techniques. They yielded age estimates of 17.08 ± 1.86 ka and 166.2 ± 21.8 ka (Lindsey, 2024). The latter date correlates with the earlier part of the Bull Lake glaciation (Madole, 1991; Kellogg and others, 2008). Areas, where the unit is mantled by eolian sediment (unit Qe), may experience hazards related to soil collapse. The unit is not a likely source of sand or gravel. Water well and geotechnical logs indicate the unit may be as much as 9 m thick, but is typically 6 m thick or less. | 01-03-02 | DMUUnit1 | Qafo | Qafo | 255-255-190 | 230-0-169 50% transparency random dot fill | DAS1 | Debris flows, landslides, and other localized mass-movement sediment | Medium | DMU14 |
| 13 | None | EOLIAN DEPOSITS | EOLIAN DEPOSITS | None | None | 01-04 | DMUHeading2 | None | None | None | None | DAS1 | None | None | DMU15 |
| 14 | Qe | Eolian deposits | Eolian deposits | Holocene and Upper Pleistocene (?) | The unit is not well exposed in the mapped area, but numerous DWR well logs and geotechnical borings record descriptions of the unit. It is comprised predominantly of silt and sand. Deposits are tan, light-yellowish brown, yellowish-brown, and olive-brown in color, massive, and homogenous. Secondary carbonate is present in older deposits. Deposits are more widespread than what is mapped, but unit Qe is locally discontinuous and contacts between Qe and other surficial deposits are difficult to identify, so they are mapped together in many places (such as unit Qafo). Colton (1978) mapped deflation basins in the northeast portion of the quadrangle that may have been eroded, in part, by wind. Northwest-southeast trending dune crests are also mapped by Colton (1978) in this area. Lidar was used to map deflation basins and dune crests in the mapped area, but topography is muted, so locations are approximate. The presence of dunes indicates a higher concentration of sand in the eolian deposits in this part of the mapped area. Elsewhere, eolian sediment may have a higher concentration of silt. In silt-dominant deposits, lenses of sand and dispersed pebble-gravel are present owing to the periodic reworking of the unit locally. Areas underlain by eolian sediment may be subject to hazards related to soil collapse or expansion, owing to the higher concentrations of clay derived from the Pierra Shale. The unit is not a likely source of sand. DWR wells and geotechnical borings record sandy silt and clay as much as 11 m thick in places, but unit Qe can be much thinner, locally. It is unclear how much thinner. Colton (1978) reports that deflation basins may be directly underlain by bedrock. Lidar imagery interpretation indicates there may be as much as 12 m of eolian sediment in the northeastern part of the mapped area, assuming bedrock is close to the ground surface underlying deflation basins. | 01-04-01 | DMUUnit1 | Qe | Qe | 254-249-194 | None | DAS1 | Eolian sediment | High | DMU16 |
| 15 | None | BEDROCK GEOLOGY | BEDROCK GEOLOGY | None | None | 02 | DMUHeading1 | None | None | None | None | DAS1 | None | None | DMU17 |
| 16 | Kp | Pierre Shale | Pierre Shale | Upper Cretaceous | Only shown on cross-sections A-A’ and B-B’ (Plate 2). All members in the quadrangle are mostly mantled by surficial deposits. Areas underlain by members of the Pierre Shale, especially those with higher proportions of claystone, siltstone, and shale, may be subject to hazards related to expansive soils, collapsible soils, and are easily eroded. Though no landslides are mapped in the quadrangle, slopes underlain by the unit may be subject to landsliding, especially where slopes are greater than 10 degrees, contain higher concentrations of clay, and are overlain by gravelly deposits. Historically, clayey members of the Pierre Shale have been mined for materials to manufacture brick and tile. Larrabee (compiler, 1947) mapped much of the clay-rich Pierre members in the quadrangle as a resource of brick and tile manufacturing materials. | 02-01 | DMUUnit1 | Kp | Kp | 153-208-153 | None | DAS1 | Clastic sedimentary rock | High | DMU18 |
| 17 | Kpu | Upper member | Upper member | Upper Cretaceous | The unit consists of easily eroded, valley-forming, gray, silty shale interbedded with sandstone. Sandstone interbeds are friable and typically yellow. The unit weathers to grayish green, gray, or light-olive brown soils. Index fossils | 02-01-01 | DMUUnit2 | Kpu | Kpu | 137-137-68 | None | DAS1 | Sandstone and mudstone | Medium | DMU19 |
| 18 | Kplr | Larimer, Richard, and Rocky Ridge members and intervening shale | Larimer, Richard, and Rocky Ridge members and intervening shale | Upper Cretaceous | The unit underlies low-lying ridges in the quadrangle. It is comprised of yellow- to tan-colored sandstone with interbedded friable shales. Shales are grayish-green, gray, or light-olive brown. Sandstones within the unit are moderately indurated to friable, medium- to coarse-grained, and weakly to very weakly bedded. Concretions containing shell hash are abundant, and | 02-01-02 | DMUUnit2 | Kplr | Kplr | 153-235-128 | None | DAS1 | Mostly sandstone | High | DMU20 |
| 19 | Kpm | Middle member | Middle member | Upper Cretaceous | The unit is comprised chiefly of erodible, valley-forming claystone and sandy siltstone. Claystones and siltstones are typically greenish gray in color. Index fossils | 02-01-03 | DMUUnit2 | Kpm | Kpm | 158-255-204 | None | DAS1 | Mostly mudstone | Medium | DMU21 |
| 24 | Kpmu | Middle to Upper members, undivided | Middle to Upper members, undivided | Upper Cretaceous | Shown on cross-section C-C’ only (Plate 2). | 02-01-04 | DMUUnit2 | Kpmu | Kpmu | 200-220-100 | None | DAS1 | Clastic sedimentary rock | High | DMU22 |
| 20 | Kph | Hygiene Sandstone | Hygiene Sandstone | Upper Cretaceous | The unit is comprised of yellowish-brown, tan, light-gray, or gray sandstone with varying degrees of induration. In the quadrangle, the Hygiene Sandstone is very weakly bedded and moderately friable. Concretions may be present in the lower part of the unit. Siltstones are interbedded with sandstones in the member. The unit underlies ridges in the southern part of the quadrangle, though the unit does not crop out well. Soils derived from the Hygiene Sandstone are typically sandy and yellowish to tan in color. Index fossil ammonites | 02-01-05 | DMUUnit2 | Kph | Kph | 128-255-0 | None | DAS1 | Mostly sandstone | High | DMU23 |
| 21 | Kpl | Lower member | Lower member | Upper Cretaceous | The unit is comprised chiefly of dark-olive brown to black shale and sandy shale. Soils derived from the unit are typically greenish brown to olive. The lower member underlies swales in the western part of the quadrangle and is poorly exposed. Bentonite beds are present in the basal part of the unit. Index fossils | 02-01-06 | DMUUnit2 | Kpl | Kpl | 153-173-128 | None | DAS1 | Mostly mudstone | High | DMU24 |
| 22 | Kn | Niobrara Formation | Niobrara Formation | Upper Cretaceous | The Smoky Hill Member of the Niobrara Formation is exposed only in sec. 4, T. 6 N., R. 69 W. on the western edge of the quadrangle. Here, the upper part of the Niobrara is a thinly bedded, fissile, shaley micritic limestone and limey shale. The color of the unit is gray and it weathers to tan. Fossils are absent from this outcrop. The contact with the Pierre Shale is distinguished by the sharp change from gray limestone to black shale. The unit is approximately 79 m thick in the area. | 02-02 | DMUUnit1 | Kn | Kn | 235-255-179 | None | DAS1 | Mostly carbonate rock | High | DMU25 |
| 25 | Kcgg | Carlile Shale, Greenhorn Limestone, and Graneros Shale, undivided | Carlile Shale, Greenhorn Limestone, and Graneros Shale, undivided | Upper and Lower Cretaceous | Includes the Codell Sandstone. Only shown on cross-section C-C’ (Plate 2). The unit is approximately 165 m thick (Colton, 1978). | 02-03 | DMUUnit1 | Kcgg | Kcgg | 204-255-48 | None | DAS1 | Sedimentary rock | High | DMU26 |
| 26 | Kd | Dakota Group | Dakota Group | Lower Cretaceous | Shown in cross-section C-C’ only (Plate 2). The unit is as much as 88 m thick in the Horsetooth Reservoir quadrangle adjacent to the west (Braddock and others, 1989). | 02-04 | DMUUnit1 | Kd | Kd | 205-205-102 | None | DAS1 | Mostly sandstone | High | DMU27 |
| 27 | JTRmj | Morrison Formation, Sundance Formation, and Jelm Formation, undivided | Morrison Formation, Sundance Formation, and Jelm Formation, undivided | Upper Jurassic and Upper Triassic | Shown in cross-section C-C’ only (Plate 2). The unit is as much as 158 m thick in the Horsetooth Reservoir quadrangle adjacent to the west (Braddock and others, 1989). | 02-05 | DMUUnit1 | JTRmj | JTRmj | 153-204-204 | None | DAS1 | Sedimentary rock | High | DMU28 |
| 28 | TRPly | Lykins Formation and Lyons Sandstone, undivided | Lykins Formation and Lyons Sandstone, undivided | Triassic and Permian | Shown in cross-section C-C’ only (Plate 2). Unit is as much as 192 m thick in the Horsetooth Reservoir quadrangle adjacent to the west (Braddock and others, 1989). | 02-06 | DMUUnit1 | TRPly | TRPly | 204-222-222 | None | DAS1 | Sedimentary rock | High | DMU29 |
| 29 | PPsif | Satanka, Ingleside, and Fountain Formations, undivided | Satanka, Ingleside, and Fountain Formations, undivided | Permian and Pennsylvanian | Shown in cross-section C-C’ only (Plate 2). Unit is as much as 382 m thick in the Horsetooth Reservoir quadrangle adjacent to the west (Braddock and others, 1989). | 02-07 | DMUUnit1 | PPsif | PPsif | 115-178-255 | None | DAS1 | Sedimentary rock | High | DMU30 |
| 32 | water | water | water | None | None | 03 | DMUUnit1 | None | water | 174-203-248 | None | DAS1 | Water or ice | High | DMU31 |
| 33 | no data | no data | no data | None | None | 04 | DMUUnit1 | no data | no data | 255-255-255 | None | DAS1 | Unmapped area | High | DMU32 |
| OBJECTID | Term | Definition | DefinitionSourceID | Glossary_ID |
|---|---|---|---|---|
| 22 | ? | a punctuation marks used to express doubt or uncertainty | DICT1 | GLO01 |
| 18 | 1 SD | 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 | GLO02 |
| 12 | Age | the length of time during which a being or thing has existed; length of life or existence to the time spoken of or referred to | DICT1 | GLO03 |
| 19 | anticline | A fold, generally convex upward, whose core contains the stratigraphically older rocks. | AGI | GLO04 |
| 24 | Bedding | A measurement convention used to describe the orientation, or attitude, of a planar geologic feature. A feature's strike is the azimuth of an imagined horizontal line across the plane, and its dip is the angle of inclination measured downward from horizontal. | AGI | GLO05 |
| 31 | Bedrock | Solid rock present beneath any soil, subsoil, sediment, or other surface cover. In some locations it may be exposed at Earth's surface. | AGI | GLO06 |
| 9 | boundary | A line that marks the limits of an area | DICT1 | GLO07 |
| 32 | Cartoline | features used to provide context in the cross section illustrations | DAS1 | GLO08 |
| 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 | GLO09 |
| 20 | CGSLURWell | City of Fort Collins geotech boring | DAS1 | GLO10 |
| 8 | 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. | AGI | GLO11 |
| 14 | crossing line | features used toprovide context in teh cross section illustrations | DAS1 | GLO12 |
| 33 | Deflation basin | A topographic basin excavated and maintained by wind erosion which removes unconsolidated material. | AGI | GLO13 |
| 25 | Deposit type | Groupings for surficial units in the CMU | DAS1 | GLO14 |
| 5 | DMUHeading1 | GeMS hierarchy formatting term | GeMS1 | GLO15 |
| 6 | DMUHeading2 | GeMS hierarchy formatting term | GeMS1 | GLO16 |
| 3 | DMUUnit1 | GeMS hierarchy formatting term | GeMS1 | GLO17 |
| 4 | DMUUnit2 | GeMS hierarchy formatting term | GeMS1 | GLO18 |
| 17 | Dune crest | The highest elevation of a dune | AGI | GLO19 |
| 26 | DWR Well | Division of Water Resources water well: Wells (bore holes) that penetrate artesian aquifers. Water will rise up the well casing to the pressure level of the aquifer. Artesian flow describes the natural flow to the surface of water from confined aquifers. | DWR | GLO20 |
| 16 | ELEV_FT | A hatch mark shown on the edges of geologic cross sections to denote the elevation in feet | DAS1 | GLO21 |
| 15 | ELEV_M | A hatch mark shown on the edges of geologic cross sections to denote the elevation in meters | DAS1 | GLO22 |
| 21 | Geotech Well | A well used as part of the investigation process carried out on site prior to construction. | DAS1 | GLO23 |
| 34 | High | of greater degree, amount, cost, value, or content than average, usual, or expected | DICT1 | GLO34 |
| 30 | leader | features used toprovide context in teh cross section illustrations | DAS1 | GLO24 |
| 28 | LUR | Larimer County Land Use Department geotech boring | DAS1 | GLO25 |
| 35 | Medium | a middle condition or degree | DICT1 | GLO35 |
| 27 | O&G Well | An oil well is a boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may be termed a gas well. | AGI | GLO26 |
| 23 | 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. | BAYLOR | GLO27 |
| 29 | Quaternary | The most recent period of geologic time that begins about 2.588 million years ago and extends to the present. It follows the Neogene Period and is divided into the Pleistocene (2.588 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to present). | AGI | GLO28 |
| 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 | GLO29 |
| 7 | surface | The topographic profile of the cross section | DICT1 | GLO30 |
| 13 | syncline | A fold of which the core contains the stratigraphically younger rocks; it is generally concave upward. | AGI | GLO31 |
| 10 | water | a colorless, transparent, odorless liquid that forms the seas, lakes, rivers, and rain and is the basis of the fluids of living organisms. | DICT1 | GLO32 |
| 11 | yr | the time taken by the earth to make one revolution around the sun | DICT1 | GLO33 |
| OBJECTID | MapProperty | MapPropertyValue | MiscellaneousMapInformation_ID |
|---|---|---|---|
| 1 | 1GeoHistory | The Fort Collins quadrangle spans three physiographic settings: the northern Colorado Piedmont section of the Great Plains, the northern margin of the Colorado Front Range, and the western edge of the Denver Basin. The city of Fort Collins is mostly within the quadrangle boundaries, as is part of the city of Loveland. The Denver Basin is an asymmetric basin formed during the Laramide Orogeny and is bounded on the west by the Rocky Mountains. The Laramide Orogeny started near the end of the Cretaceous period, contemporaneous with the final transgressions and regressions of the Western Interior Seaway. The final transgressive and regressive sequences are recorded by the sediments comprising the members of the Pierre Shale (unit Kp), Fox Hills Sandstone, and Laramie Formation; the latter two are not mapped in the quadrangle but are present in the Severance quadrangle to the east of the mapped area (Marr and others, 2025). Bedrock in the Fort Collins quadrangle includes the lower (unit Kpl), Hygiene Sandstone (unit Kph), middle (unit Kpm), Larimer, Richard, and Rocky Ridge (unit Kplr), and upper (unit Kpu) members of the Pierre Shale, as well as the upper part of the Niobrara Formation (unit Kn), which is present only along the western border. | MMI01 |
| 3 | 2GeoHistory | Bedrock units west of the quadrangle are moderately dipping and resistant units form hogbacks like those elsewhere along the Colorado Front Range. Unit Kn forms low-lying hogbacks close to the western border of the quadrangle and dips at about 25 degrees to the east. Dips decrease quickly to the east. In the southern part of the mapped area, units Kph, Kplr, and Kpu dip approximately 12 to 16 degrees east and strike north-northeast. In the middle and northern parts of the mapped area, units Kplr and Kpu dip approximately 9 to 10 degrees and strike more consistently north. | MMI03 |
| 4 | 3GeoHistory | Minor faulting could account for the slightly steeper dips and the slightly more northeast-trending strike of the units in the southern part of the mapped area. A minor, apparently strike-slip or oblique-slip fault mapped by Braddock and others (1989) may project from the southern part of the Horsetooth Reservoir quadrangle into the Fort Collins quadrangle and could account for the difference in dips between the northern and southern parts of the mapped area. Owing to the weak nature of the lower member of the Pierre Shale, the fault likely attenuates quickly, and, with no opportunities to collect structural data in the area of the fault in the Fort Collins quadrangle because of the poor exposure, the fault is not mapped. In the northern part of the mapped area, Weimer (1996) mapped an anticline and dome, the southern end of which projects into the Fort Collins quadrangle. There are well logs north of the quadrangle that show bedrock dipping shallowly to the east and a marked increase in dip around the area of Weimer’s anticline axis and dome. Workman and others (2018) mapped this structure as a Laramide-aged syncline and anticline pair and that is reflected in cross-section C-C’. The few oil and gas wells in the mapped area are only located near the very southern extent of the structures. There is little control on the precise location and geometry of any structures underlying the quadrangle. | MMI04 |
| 5 | 5GeoHistory | Kellogg and others (2008) place the Bull Lake glaciation (marine oxygen isotope stage (MIS) 6) and the associated Louviers Alluvium around 170-120 ka. Madole (1991) considers the Bull Lake glaciation to be 200 to 130 ka. The Louviers Alluvium also includes MIS 5-aged sediment, 70-130 ka (Lisiecki and Raymo, 2005; Workman and others, 2018). Kellogg and others (2008) give tentative, relative ages of 390-320 ka and 300-220 ka to the Slocum Alluvium in the Denver area. More geochronology and mapping are necessary to fully constrain the ages of these deposits. | MMI05 |
| 6 | 7GeoHistory | There are four alluvial units younger than unit Qafo in the mapped area. On cross-section B-B’, possibly three distinct terraces underlain by unit Qa4 are mapped on the northeast side of the Poudre River. Unit Qa3 forms an inset strath terrace relative to unit Qa4. In the Fort Collins quadrangle, and similar to other areas near the foothills of the northern Colorado Piedmont, unit Qa2 subsequently incised Qa3 to create a nested fill terrace, leaving remnants of Qa3 preserved as an unpaired, higher terrace adjacent to the modern Poudre River. Unit Qa1 is currently incising into unit Qa2, leaving low-lying terraces that are underlain by unit Qa2, adjacent to the river. | MMI06 |
| 7 | 8GeoHistory | These relationships are identified in cross-section B-B’. The single Qa4 deposit mapped on the southwestern side of the Poudre River is likely paired with the youngest (lowest) Qa4 deposit on the northeastern side, owing to similar basal elevations. Interpretations and correlations of these deposits have a high degree of uncertainty because they are buried by eolian deposits (unit Qe) and owing to the proximity to the Box Elder Creek and the Poudre River confluence. The top of the middle terrace, underlain by Qa4 terrace on the north side of the Poudre River (on the east side of cross-section B-B’), is approximately 20 m above the modern Poudre River. Kellogg and others (2008) report that the top of the correlative Louviers Alluvium is around 20 m. Additionally, Kellogg and others (2008) speculate that the Louviers Alluvium (unit Qa4) underlies unit Qe in the quadrangle. The alluvium underlying the highest terrace furthest east on cross-section B-B’ is interpreted as unit Qa4 owing to how closely inset the lower (younger) terraces are. Typically, the next oldest alluvial unit in the sequence, unit Qg1, exists on a strath with bedrock well-exposed from subsequent erosion. Interpretations from DWR well logs indicate that, while the unit does exist on a strath, subsequent erosion and aggradation did not fully expose the bedrock at this location before the next youngest terrace was abandoned. | MMI07 |
| 8 | 9GeoHistory | A cutbank in NW ¼, sec. 18, T. 7 N., R. 68 W., exposes approximately 3 m of unit Qa4 and the underlying Pierre Shale. At this exposure, an optically stimulated luminescence (OSL) sample, FC-KF-23-01, was collected approximately 2 m below ground surface (bgs). It yielded a SAR-OSL age estimate of 76,820 ± 5,210 yrs. This age is correlative with later MIS 5, possibly MIS 4 (Lisiecki and Raymo, 2005). Deposits of this age do not commonly form the upper parts of terraces along the Front Range and in the northern Piedmont. Colorado Geological Survey work has confirmed that Qa3-aged (MIS 2) sediments typically bury MIS 4, MIS 5, and locally MIS 6 (Bull Lake) deposits. Sampling and OSL dating in the Kersey quadrangle (Lindsey and Palkovic, 2022) and Gowanda quadrangle (Keller and others, 2019) indicate a series of deposits spanning the time between the end of the Bull Lake glaciation (approximately 130 ka; Madole, 1991) and the beginning of the Pinedale glaciation (approximately 30 ka (Nelson and others, 1979) or possibly earlier (Madole and others, 2010)). Some of the intermediate dates, ranging from 42 to 87 ka, indicate that some deposits may be correlative with MIS 3, 4, and 5 (Lisiecki and Raymo, 2005). Kellogg and others (2008) mapped MIS 5-aged and MIS 6-aged deposits as the Louviers Alluvium, which is correlative with unit Qa4. | MMI08 |
| 9 | 10GeoHistory | Unit Qa3 is exposed in places adjacent to the Poudre River and its major tributaries, as well as in quarries underlying unit Qa2. Exposed terraces range from 3 to 8 m above the modern Poudre River channel. In the Fort Collins quadrangle, four samples were collected from an exposure in Strang Quarry in the NW ¼, sec. 33, T. 7 N., R. 68 W., and analyzed by OSL techniques. The older two samples, FC-SCQ-23-01 and FC-SCQ-23-04, yielded age estimates of SAR-OSL 9,665 ± 415 yrs and SAR-OSL 16,025 ± 975 yrs, respectively. Sample FC-SCQ-23-04 is correlative with the Pinedale Glaciation, which ended by 12 ka (Madole and Shroba, 1979). An additional, more recent study suggests that complete deglaciation occurred by 14 ka in the Arkansas River valley (Schweinsberg and others, 2020). Sample FC-SCQ-23-01 may be correlative with a period of glacial outwash deposition that occurred as glaciers retreated. Prior studies indicate that Pinedale outwash deposition likely ended around 10 ka (Holliday, 1987; Kellogg and others, 2008). | MMI09 |
| 10 | 11GeoHistory | The younger two samples collected from the Strang Quarry, FC-SCQ-23-02 and FC-SCQ-23-03, yielded age estimates of SAR-OSL 6,100 ± 210 yrs and SAR-OSL 5,085 ± 325 yrs, respectively, and both post-date the Pinedale glaciation. These samples and their respective deposits are interpreted as correlative with unit Qa2. However, sample FC-SCQ-23-01 (unit Qa3) is higher in stratigraphic order (0.8 m bgs) than FC-SCQ-23-03 (unit Qa2, 1.9 m bgs). There are two possible explanations for this: 1. Unit Qa2 and unit Qa3 comprise nested terrace deposits and the quarry exposure shows a complex relationship of channel cut and fills throughout the depositional history of these units. While FC-SCQ-23-01 may be higher stratigraphically, these samples were not taken in direct vertical succession and are slightly offset laterally. It is possible that a lower portion of a younger channel cut and fill comprised of unit Qa2 was sampled at site FC-SCQ-23-03, yielding an age estimate of 5,085 ± 325 yrs that appears lower in the stratigraphic sequence than the age estimate from FC-SCQ-23-01, which is 9,665 ± 415 yrs; or, 2. The age estimate is incorrect. Sample FC-SCQ-03 has the highest overdispersion of the OSL samples collected at the Strang Quarry site: 27 ± 4%. Higher overdispersion values (>20%) may indicate multiple age populations owing to partial bleaching of the quartz grains or from sediment mixing (Steve Forman, written commun., 2025). Sample FC-SCQ-23-01 has an overdispersion of 21 ± 3. Option 2 seems most likely because sample FC-SCQ-03 was collected very close to an erosional contact between lower gravelly alluvium generally considered to be unit Qa3 and upper, finer-grained alluvium considered to be Qa2. | MMI10 |
| 11 | 1GeoHazard | The shaley, clayey, and muddy Cretaceous bedrock in the mapped area can contain naturally occurring, high-swell clays. These clays pose a hazard when they are not properly mitigated. Mitigation typically includes over-excavation of the deposit. If these soils are not properly treated, when structures with conventional foundations are built and soils are wetted, the clays will absorb the water and expand. The soil expansion exerts compressional forces that may cause damage to the structure. Additionally, when the clays dry after being wetted, they contract and decrease in volume (referred to as shrink-swell), and structures are not designed to accommodate these volume changes over time. Some Quaternary deposits, such as units Qa and Qe, are fine-grained and loosely consolidated, owing to an excess of interstitial space in the deposit. These deposits are referred to as collapsible soils. If loosely consolidated sediments are wetted and compressed, the interstitial space is reduced irregularly through the deposit. Infrastructure built on collapsible soils may be subject to irregular settlement if these soils are not properly treated and compacted prior to construction. | MMI11 |
| 13 | 2GeoHazard | Though none are mapped in the quadrangle, due to the relatively low strength of the clayey members of the Pierre Shale, landslides can occur even on lower gradient slopes, especially where Quaternary deposits overlie bedrock. Several factors can contribute to landslide initiation in these geological conditions: 1. The clayey bedrock tends to be more easily erodible than the overlying Quaternary units, leading to undercut, over-steepened slopes; and, 2. Groundwater accumulating at the contact between Quaternary deposits and underlying clayey, less permeable bedrock can cause a reduction of internal friction of the units, leading to slope destabilization. These slopes can become easily destabilized by human activity that either cuts or erodes the toes of slopes without properly reinforcing or stabilizing the excavation. Unit Qaf consists of alluvial-fan and debris-flow deposits and sediments deposited by floods. Alluvial-fan, debris-flow, and flood processes can carry large sediment loads and clasts large enough to impart considerable damage to infrastructure. In the quadrangle, areas underlain by unit Qaf are prone to flooding, sediment inundation, and erosion. Much of the area underlain by units Qa1 and Qa2 is within the FEMA 1% annual chance of flooding (Zone AE), and some have a 0.2% annual chance floodway (URL link in references). Other areas that may be prone to seasonal flooding include those underlain by unit Qa. Flooding can pose hazards via extensive erosion or sediment inundation. Other areas that may be prone to erosion include areas underlain by easily eroded bedrock, like the shaley and clayey members of the Pierre Shale. | MMI13 |
| 15 | 1GeoHazardSubTitle | Expansive and collapsible soils: | MMI15 |
| 16 | 2GeoHazardSubTitle | Mass-wasting, flooding, and erosion: | MMI16 |
| 20 | 4GeoHistory | Much of the quadrangle’s bedrock is mantled by surficial sediments deposited repeatedly during the Pleistocene and Holocene. The oldest Quaternary sediments in the mapped area, unit Qafo, were deposited by alluvial-fan processes over broad areas in the western and central portions of the quadrangle. Unit Qafo in the mapped area is correlative with Qafo in the southern adjacent Loveland quadrangle based on morphology and depositional processes. These deposits are mapped as Slocum Alluvium by Colton (1978), Kellogg and others (2008), Cole and Braddock (2009), and Workman and others (2018). Defining a specific age for Middle Pleistocene and older deposits is difficult near the foothills as streams likely undergo repeated cycles of deposition, erosion, and avulsion before an alluvial surface is abandoned (Riihimaki and others, 2006). A sample collected from unit Qafo in the Loveland quadrangle and analyzed by infrared stimulated luminescence techniques yielded age estimates of 166.2 ± 21.8 ka (Lindsey, 2024). The age estimate from this sample indicates parts of unit Qafo could be correlative with the Louviers Alluvium (Bull Lake glaciation) of Colton (1978), Kellogg and others (2008), Cole and Braddock (2009), and Workman and others (2018). | MMI20 |
| 21 | 6GeoHistory | Unit Qafo underlies fan surfaces at several levels in the landscape, indicating ancestral drainages likely experienced several distinct periods of deposition and erosion, with younger deposits underlying lower surfaces in the landscape. Since the depositional surfaces were abandoned, periodic downcutting has formed minor, ephemeral channels that dissect fan surfaces and flow into the Cache la Poudre River (hereafter referred to as the Poudre River). These ephemeral streams have and continue to deposit alluvial sediments, mapped as Qa, in and near the bases of their channels. | MMI21 |
| 24 | 1Resources | The quadrangle lies outside of any major oil and gas and groundwater producing areas. The Wattenberg Field, a world-class oil and gas-producing area, lies east and southeast of the mapped area (Weimer, 1996). The major bedrock aquifer-bearing units are also located outside the mapped area, to the east; however, local, perched groundwater may be present in Quaternary units that overlie clayey and shaley members of the Pierre Shale. The clays in the bedrock unit function as natural barriers to downward groundwater movement. The Poudre River channel is heavily modified by human activity and quarrying of the stream’s gravelly alluvium is extensive. Quarrying operations typically target the gravelly alluvium of unit Qa3. Reclaimed quarries span the length of the channel in the mapped area and now serve as fishing ponds and wildlife habitat. The quarried aggregate is used in road base and construction operations in the region. Units Qafo and Qa2 may be local sources of gravel or sand aggregate; however, unit Qa2 is often treated as overburden in quarrying operations and removed to access the underlying gravel. Additionally, the gravel of unit Qafo may not be extensive enough or clean enough to be economically viable. Schwochow and others (1974) list parts of unit Qafo as an A2 deposit and Qa2 as an F1 deposit. A2 deposits are alluvial-fan deposits that are “gently sloping, fan-shaped deposits of gravel, sand, silt, and clay produced by a stream that issued or issues from a narrow valley or point source onto an open plain or valley. Includes erosional remnants of fan deposits.” and there may be gravel with significant silt, clay, and rock with calcium carbonate. F1 deposits are floodplain deposits that may have clean gravel aggregate sources. Units Qa, Qaf, Qe, and Qa1 are not likely sources of sand or gravel aggregate because they are not typically well-sorted and are too limited in extent to serve as commercially viable resources. | MMI24 |
| 25 | ACKNOWLEDGEMENTS | The following people provided a detailed review that benefited these mappers and map products extensively: Ralph Shroba (U.S. Geological Survey Emeritus and CGS employee), John Singleton (Associate Professor, Colorado State University), Joanna Redwine (STATEMAP Program Manager), and Matt Mogan (CGS Director and State Geologist). Caitlin Bernier (Pangaea Geospatial) performed map layout and production. Steve Forman (Baylor University Geoluminescence Lab) performed OSL analysis. Todd Juhasz and other staff with the City of Fort Collins Natural Areas helped these authors with Natural Areas permits and land access. Todd Juergens and other employees with Larimer County helped coordinate access to quarry exposures which allowed for geochronology sampling and provided important data to the project. Scott Benton, Dave Betley, and other staff with the City of Fort Collins provided detailed geotechnical data that help supplement areas that were not field-accessible. | MMI25 |
| 26 | Map Production | Contacts are difficult to identify in the field given how extensive human development is in the Fort Collins area. Many contacts were mapped using 1-m resolution lidar-derived maps and 2- to 5-ft contours. The authors used well-log and boring-log data to estimate some unit contacts and develop cross-sections. Well and boring location accuracy is unknown but assumed to be relatively good. Wells and borings are projected to the cross-section lines. With limited surface exposure of Quaternary and bedrock units, the cross-sections are largely illustrative and may not be accurate, locally. | MMI26 |
| 27 | 12GeoHistory | Unit Qa1 underlies the modern Poudre River and some very low-lying (1 to 2 m-high) terraces adjacent to the channel in the river’s floodplain. Much of the lower river valley has been modified and quarried for gravel. Eolian sediment (unit Qe) has been deposited and reworked periodically by later eolian processes and (or) fluvial transport, through the Holocene and possibly during the Late Pleistocene. Subtle dune crests in the northeastern part of the mapped area indicate a northwest to southeast wind direction. These deposits, given the presence of dune features, likely have a higher concentration of sand than other eolian deposits in the quadrangle. | MMI27 |
| 28 | Ref1 | Birkeland, P.W., 1999, Soil and Geomorphology, Third Edition: Oxford University Press, 430 p. | MMI28 |
| 29 | Ref2 | Braddock, W.A., Calvert, R.H., O’Connor, J.T., and Sann, G.A., 1989, Geologic map of the Horsetooth Reservoir quadrangle, Larimer County, Colorado: U.S. Geological Survey, Geologic Quadrangle Map GQ-1625, scale 1:24,000. https://doi.org/10.3133/gq1625 | MMI29 |
| 30 | Ref3 | CO DWR (Colorado Division of Water Resources), 2023, Driller’s logs incorporated with water-well permits. https://dwr.colorado.gov/services/data-information/gis | MMI30 |
| 31 | Ref4 | CO ECMC (Colorado Energy and Carbon Management Commission), 2023, Colorado oil and gas Commission data download: Colorado oil and gas Commission, monthly production by county. https://cogccmap.state.co.us/cogcc_gis_online/ | MMI31 |
| 32 | Ref5 | Cole, J.C., and Braddock, W.A., 2009, Geologic map of the Estes Park 30’ x 60’ quadrangle, north-central Colorado: U.S. Geological Survey, Scientific Investigations Map SIM 3039, scale 1:100,000. http://doi.org/10.3133/sim3039 | MMI32 |
| 33 | Ref6 | Colton, R.B., 1978, Geologic map of the Boulder-Fort Collins-Greeley area, Front Range urban corridor, Colorado: U.S. Geological Survey, Miscellaneous Investigations Series Map I-855-G, scale 1:100,000. https://ngmdb.usgs.gov/Prodesc/proddesc_9734.htm | MMI33 |
| 34 | Ref7 | FEMA, FEMA flood map service center: access in February 2023 at: https://msc.fema.gov/portal/home | MMI34 |
| 35 | Ref8 | 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. https://doi.org/10.1016/j.quageo.2012.04.020 | MMI35 |
| 36 | Ref9 | Holliday, V.T.,1987, Geoarchaeology and late Quaternary geomorphology of the middle South Platte River, northeastern Colorado: Geoarchaeology, v. 2, p. 317-329. https://doi.org/10.1002/gea.3340020404 | MMI36 |
| 37 | Ref10 | Keller, S.M., Lindsey, K.O., and Morgan, M.L., 2019, Geologic map of the Gowanda quadrangle, Weld County, Colorado: Colorado Geological Survey, OF-19-02, scale 1:24,000. https://doi.org/10.58783/cgs.of1902.jukd7298 | MMI37 |
| 38 | Ref11 | Kellogg, K.S., Shroba, R.R., Bryant, Bruce, Premo, W.R., 2008, Geologic map of the Denver West 30’ x 60’ quadrangle, North-Central Colorado: U.S. Geological Survey, Scientific Investigations Map 2000, 1:100,000. http://doi.org/10.3133/sim3000 | MMI38 |
| 39 | Ref12 | Larrabee (compiler), D.M., Clabaugh, S.E., Griffitts, W.R., Fischer, E.C., Fox, E.L., Bryson, R.P., Weeks, R.A., Varnes, D.J., and Rolnick, L.S., 1947, Construction materials and nonmetallic mineral resources of Colorado: Missouri Basin Study, no. 10, scale 1:500,000. https://doi.org/10.3133/mb10 | MMI39 |
| 40 | Ref13 | Liang, P., and Forman, S.L., 2019, LDAC – An excel-based program for luminescence equivalent dose and burial age calculations: Ancient TL, v. 37, no. 2. | MMI40 |
| 41 | Ref14 | Lindsey, K.O., 2024, Geologic map of the Loveland quadrangle, Larimer County, Colorado: Colorado Geological Survey, OF-23-03, scale 1:24,000. https://doi.org/10.58783/cgs.of2303.lvwf5542 | MMI41 |
| 42 | Ref15 | Lindsey, K.O., and Palkovic, M.J., 2022, Geologic map of the Kersey quadrangle, Weld County, Colorado: Colorado Geological Survey, OF-20-06, scale 1:24,000. https://doi.org/10.58783/cgs.of2006.vdlh3013 | MMI42 |
| 43 | Ref16 | Lisiecki, L.E., and Raymo, M.E., 2005, A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records: Paleoceanography, v. 20, PA1003, 17 p. https://doi.org/10.1029/2004PA001071 | MMI43 |
| 44 | Ref17 | Machette, M.N., 1985, Calcic soils of the southwestern United States: Geological Society of America, Special Paper 203, 22 p. https://doi.org/10.1130/SPE203-p1 | MMI44 |
| 45 | Ref18 | Madole, R.F., 1991, Colorado Piedmont, | MMI45 |
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