Surficial geologic map database for the Blanca Peak, Walsenburg, Trinidad, and Alamosa 30' x 60' quadrangles, Colorado

This data release presents geologic map data for the surficial geology of the Blanca Peak, Walsenburg, Trinidad, and Alamosa 30' x 60' quadrangles, Colorado, and an adjacent area to the north of the Blanca Peak quadrangle. The map area lies within two physiographic provinces of Fenneman (1928): the Southern Rocky Mountains Province, and the Great Plains Province, Raton Section. Geologic mapping is mostly compiled from published geologic map data sources ranging from 1:24,000 to 1:250,000 scale, with limited new interpretive contributions. Gaps in map compilation are related to a lack of published geologic mapping at the time of compilation, and not necessarily a lack of surficial deposits. Much of the geology incorporated from published geologic maps is adjusted based on digital elevation model and natural-color image data sources to improve spatial resolution of the data. Spatial adjustments and new interpretations also eliminate mismatches at source map boundaries.

This data set represents only the surficial geology, defined as generally unconsolidated to moderately consolidated sedimentary deposits that are considered Quaternary or partly Quaternary in age, and faults that are either known or suspected as having been active during the Quaternary. Bedrock and sedimentary material directly deposited as a result of volcanic activity are not included in this database, nor are bedrock faults not known or suspected as having been active during the Quaternary. Map units in these quadrangles include alluvial; colluvial; alluvial/colluvial; glacial; eolian sand; loess; mass-wasting; groundwater/spring discharge; and playa, lake, and wetland deposit types.

The target scale for this map compilation is about 1:100,000, but the detail of geologic mapping varies from about 1:50,000- to 1:250,000-scale depending on the scale of published geologic maps available at the time of compilation, and for new mapping, the resolution of geologic features on available basemap data. Map units are organized within geologic provinces as described by the Seamless Integrated Geologic Mapping (SIGMa) (Turner and others, 2022) extension to the Geologic Map Schema (GeMS) (USGS, 2020). For this data release, first order geologic provinces are the physiographic provinces of Fenneman (1928), which reflect the major geomorphological setting affecting depositional processes. Second order provinces are physiographic sections of Fenneman (1928) if present. Third and fourth order provinces are defined by deposit type.

Attributes derived from published source maps are recorded in the map unit polygons to preserve detail and allow database users the flexibility to create derivative map units. Map units constructed by the authors are based on geologic province, general deposit type and generalized groupings of minimum and maximum age to create a number of units typical for geologic maps of this scale.

Polygons representing map units were assigned a host of attributes to make that geology easily searchable. Each polygon contains a general depositional process (‘DepositGeneral’) as well as three fields that describe more detailed depositional processes responsible for some deposition in that polygon (‘LocalGeneticType1’ – ‘LocalGeneticType3’). Three fields describe the materials that make up the deposit (‘LocalMaterial1’ – ‘LocalMaterial3’) and the minimum and maximum chronostratigraphic age of a deposit is stored in the ‘LocalAgeMin’ and ‘LocalAgeMax’ fields, respectively. Where a polygon is associated with a prominent landform or a formal stratigraphic name the ‘LocalLandform’ and ‘LocalStratName’ fields are populated. The field ‘LocalThickness’ provides a textual summary of how thick a source publication described a deposit to be. Where three fields are used to describe the contents of a deposit, we attempt to place descriptors in a relative ordering such that the first field is most prominent, however for remotely interpreted deposits and some sources that provide generalized descriptions this was not possible. Values within these searchable fields are generally taken directly from source maps, however we do perform some conservative adjustments of values based on observations from the landscape and/or adjacent source maps. Where new features were interpreted from remote observations, we derive polygon attributes based on a conservative correlation to neighboring maps.

Detail provided at the polygon level is simplified into a map unit by matching its values to the DescriptionOfMapUnits table. Specifically, we construct map units within each province based on values of ‘DepositGeneral’ and a set of chronostratigraphic age bins that attempt to capture important aspects of Quaternary landscape evolution. Polygons are assigned to the map unit with a corresponding ‘DepositGeneral’ and the narrowest chronostratigraphic age bin that entirely contains the ‘LocalAgeMin’ and ‘LocalAgeMax’ values of that polygon. Therefore, users may notice some mismatch between the age range of a polygon and the age range of the assigned map unit, where ‘LocalAgeMin’ and ‘LocalAgeMax’ (e.g., Holocene – Holocene) may define a shorter temporal range than suggested by the map unit (e.g., Holocene – late Pleistocene). This apparent discrepancy allows for detailed information to be preserved in the polygons, while also allowing for an integrated suite of map units that facilitate visualization over a large region.

References Cited in Summary and Purpose:
 
Brock, J., Berry, K., Faulds, J., Berg, R., House, K., Marketti, M., McPhee, D., Schmidt, K., Schmitt, J., Soller, D., Spears, D., Thompson, R., Thorleifson, H., and Walsh, G., 2021, Renewing the National Cooperative Geologic Mapping Program as the Nation’s authoritative source for modern geologic knowledge: U.S. Geological Survey Open-File Report 2021–1013, 10 p., accessed April 2023, at https://doi.org/10.3133/ofr20211013.
 
Fenneman, N.M., 1928, Physiographic divisions of the United States: Annals of the Association of American Geographers, v. 18, no. 4, pp. 261-353, accessed June 2023 at https://doi.org/10.2307/2560726.
 
Turner, K.J., Workman, J.B., Colgan, J.P., Gilmer, A.K., Berry, M.E., Johnstone, S.A., Warrell, K.F., Dechesne, M., VanSistine, D.P., Thompson, R.A., Hudson, A.M., Zellman, K.L., Sweetkind, D., and Ruleman, C.A., 2022, The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS): U.S. Geological Survey Scientific Investigations Report 2022–5115, 33 p., accessed December 2022 at https://doi.org/10.3133/sir20225115.
 
U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema)—A standard format for the digital publication of geologic maps: U.S. Geological Survey Techniques and Methods, book 11, chap. B10, 74 p., accessed March 2023, athttps://doi.org/10.3133/tm11B10.