U.S. Department of the Interior Scientific Investigations Map 3475 U.S. Geological Survey Sheet 2 of 2 DESCRIPTION OF MAP UNITS Qao Older alluvium, undivided (middle to early? Pleistocene)—Massive to phic features and colluvium and eolian silt infilling of depressions. Kelson, K.I., 1986, Long-term tributary adjustments to base-level lowering in northern Ruleman, C., and Machette, M.N., 2007, An overview of the Sangre de Cristo fault well-stratified, poorly to well sorted, subangular to subrounded silty, Exposed granitic boulders are generally rounded and weathered with Rio Grande rift, New Mexico: Albuquerque, New Mexico, University of New system and new insights to interactions between Quaternary faults in the northern [Surficial units have been mapped and differentiated based on stratigraphic and crosscut- sandy pebble-cobble gravel with interbedded eolian silt and alluvial sand grussification of their outer surfaces. Till forms relatively dissected and Mexico, M.S. thesis, 210 p. Rio Grande rift, chap. J, in Machette, M.N., Coates, M.M., and Johnson, M.L., eds., Qa/Qfp/Qaa ting relationships, geomorphic characteristics such as degree of preservation of original layers and lenses. Deposits locally contain large, subrounded boulders subdued lateral moraines adjacent to, and outboard of, the Pinedale Kelson, K.I., and Bauer, P., 2006, Preliminary geologic map of the Arroyo Hondo 2007 Rocky Mountain Section Friends of the Pleistocene Field Trip—Quaternary depositional landform, pedogenic (soil) development, and correlated and inferred 1 exceeding 1 m in diameter proximal to range fronts and glaciated lateral moraines around the Blanca Peak massif. An age of 167–95 ka is quadrangle, Taos County, New Mexico: New Mexico Bureau of Geology and Geology of the San Luis Basin of Colorado and New Mexico, September 7–9, 2007: MIS 2 (30−11,700 ka) regional chronologies from multiple Quaternary chronologic proxies (table 1). Imagery Qay drainages. Deposits generally have well developed argillic soils and assigned to these deposits (generally, MIS 6 of Lisiecki and Raymo, Mineral Resources Open-file Digital Geologic Map OF–GM 116, scale 1:24,000, U.S. Geological Survey Open-File Report 2007–1193, p. 187–197, accessed January MIS 5,4,3 (126−30 ka) and elevation data used for geologic mapping was generated from multiple 1.25-meter/ common stage II–IV pedogenic carbonate development, with stage 2005) on the basis of cosmogenic-nuclide-exposure ages on correlative accessed November 28, 2020, at 13, 2021, at https://pubs.usgs.gov/of/2007/1193/. MIS 6 (191−126 ka) pixel lidar (light detection and ranging) surveys across the region (see figures 1 and 2 Qai IV pedogenic development not uncommon (carbonate content exceeding Bull Lake age geomorphic surfaces in the northern upper Arkansas River https://geoinfo.nmt.edu/publications/maps/geologic/. Ruleman, C.A., Machette, M.N., Thompson, R.A., Miggins, D.P., Goehring, B.M., and on sheet 1)] MIS 7 (243−191 ka) 40% in overlying loess cap and gravels). See table 1 for unit pedogenic basin (Kellogg and others, 2017). Estimated thickness 10–70 m Kelson, K.I., Bauer, P.W., and Thompson, R., 2008, Geologic map of the Guadalupe Paces, J.B., 2016, Geomorphic evolution of the San Luis Basin and Rio Grande in MIS 8 (300−243 ka) carbonate development and regional correlation with other early to Mountain 7.5 minute quadrangle map, Taos County, New Mexico: New Mexico southern Colorado and northern New Mexico, in Keller, S.M., and Morgan, M.L., SURFICIAL DEPOSITS Qtpb Till of Pre-Bull Lake glaciation (middle and early? Pleistocene)—Massive Qao3 middle Pleistocene gravel deposits. Clast composition is predominantly Bureau of Geology and Mineral Resources Open-file Digital Geologic Map eds., Unfolding the geology of the West: Geological Society of America Field Guide to weakly stratified, pebble to boulder gravel mantling ridge crests and MIS 9 (337−300 ka) ANTHROPOGENIC DEPOSITS locally derived Proterozoic metamorphic and intrusive and Tertiary OF–GM 168, accessed March 4, 2021, at 44, p. 291–334. [Also available at https://doi.org/10.1130/9780813700441.] older geomorphic surfaces. Locally contains lenses of pebbly sand and MIS 10 (374−337 ka) volcanic rocks. Mostly deposited as alluvial fans and pediment slope- https://geoinfo.nmt.edu/publications/maps/geologic/ofgm/details.cfml?volume=168. Ruleman, C., Shroba, R., and Thompson, R., 2007, Field trip day 3, Quaternary geology mw Mine waste deposits (latest Holocene)—Unconsolidated to loosely silty sand with boulders in a silty clay matrix, such as along Burnt Gulch wash gravel veneers, but also forms large alluvial aprons prograding Kirkham, R.M., Keller, J.W., Price, J.B., and Lindsay, N.R., 2006, Geologic map of the of Sunshine Valley and associated neotectonics along the Latir Peaks section of the compacted rubble composed of silt, sand, rock, and waste rock and Rock Creeks on the north side of Greenie Mountain and the Alamosa Qao2 sequentially into lower lake shoreline elevations associated with the southern half of the Culebra Peak quadrangle, Costilla and Los Animas Counties, southern Sangre de Cristo fault zone, in Machette, M.N., Coates, M.M., and commonly found adjacent to mine workings such as shafts, adits, and River at Terrace Reservoir, in the southwest corner of mapped area. draining of Lake Alamosa during the interval of approximately 400– Colorado: Colorado Geological Survey Open-file Report OF–05–3, scale 1:24,000, Johnson, M.L., eds., 2007 Rocky Mountain Section of the Friends of the Pleistocene MIS 11 (424−374 ka) glory holes mainly at the Orient Mine location just north of Valley View Clasts are mostly poorly sorted to unsorted, subangular to subrounded 200 ka. Geomorphic upper surfaces of unit are commonly roughly planar accessed November 28, 2020, at https://coloradogeologicalsurvey.org/publications/. Field Trip-Quaternary Geology of the San Luis Basin of Colorado and New Mexico: MIS 12 (478−424 ka) Hot Springs, but found throughout the surrounding mountains, most pebbles, cobbles, and boulders of locally derived Proterozoic and include thin eolian silt veneers. Many clasts are weathered with iron Kirkham, R.M., Lufkin, J.L., Lindsay, N.R., and Dickens, K.E., 2004, Geologic map of U.S. Geological Survey Open-File Report 2007–1193, p. 111–133, accessed being too small for display on this geologic map. Lithologies vary metamorphic and Tertiary volcanics. Boulders are commonly greater 2 staining and desert varnish. Deposits are generally preserved on the the La Valley quadrangle, Costilla County, Colorado: Colorado Geological Survey December 28, 2020, at https://pubs.usgs.gov/of/2007/1193/. 444−385 ka Lake Alamosa highstand depending on available rock sources, but are predominantly Proterozoic than 1 m in diameter, and locally exceed 3 m (Minor and others, 2019). maximum aggradation surfaces along stream drainages now represented Open-file Report OF–04–08, scale 1:24,000, accessed January 13, 2021, at Ruleman, C.A., Thompson, R.A., Shroba, R.R., Anderson, M., Drenth, B.J., Rotzien, J., Qao1 metamorphic and Tertiary volcanic rocks. Abandoned mining equipment Clasts are commonly deeply weathered and oxidized thus forming an by gently basinward sloping interfluves and inset benches capped by https://coloradogeologicalsurvey.org/publications/geologic-map-la-valley- and Lyon, J., 2013, Late Miocene–Pleistocene evolution of a Rio Grande Rift and other scrap metal is common around and within deposits. Estimated overlying grussified residium with an A/C soil profile. Deposits are gravel veneer. Apparent neotectonic displacement of the older gravels quadrangle-costilla-colorado. subbasin, Sunshine Valley–Costilla Plain, San Luis Basin, New Mexico and thickness several meters (m) to 10 m typically poorly exposed, mantled by thick soil and bouldery colluvium, ? ? ? ? makes it difficult to accurately correlate deposits across basin-margin Kirkham, R.M., Shaver, K.C., Lindsay, N.R., and Wallace, A.R., 2003, Geologic map of Colorado, in Hudson, M.R., and Grauch, V.J.S., eds., New perspectives on Rio 3 creating a smooth abandoned geomorphic surface with large boulders 631 ka Lava Creek B ash af Artificial fill (latest Holocene)—Consists of silt, sand, and cobble- to fault zones; thus we attempt to provide a maximum and minimum age the Taylor Ranch quadrangle, Costilla County, Colorado: Colorado Geological Grande Rift Basins—From tectonics to groundwater: Geological Society of America (tors, knockers, and erratics?) of local country rock protruding as much boulder-size fragments of unconsolidated to loosely compacted gravel for these older gravels. Previous work by McCalpin (1981, 1982), Survey Open-file Report OF–03–15, scale 1:24,000, accessed January 13, 2021, at Special Paper 494, p. 47–73. [Also available at https://doi.org/10.1130/SPE494.] as 1 m above the soil surface. Unit correlative with units Qtpb of and/or broken and redistributed country rock and engineered material Machette (1985), Kelson (1986), Pazzaglia and Wells (1990), Kelson https://coloradogeologicalsurvey.org/publications/geologic-map-taylor-ranch- Sarna-Wojcicki, A.M., Pringle, M.S., Jr., and Wijbrans, J., 2000, New 40Ar/39Ar age of the Kellogg and others (2017) and Lindsey and others (1984, 1985), used primarily for stabilizing slopes around and within gravel borrow and Bauer (2006), Machette and others (2007, 2013), and Ruleman and quadrangle-costilla-colorado. Bishop Tuff from multiple sites and sediment rate calibration for the Qtpb/QTd of Minor and others (2019), and QTd of Kirkham and others pits and local landfills. Clast and rubble lithologies are chiefly others (2007, 2013, 2016, 2019) established a framework in which Knepper, D.H., 1974, Tectonic analysis of the Rio Grande rift zone, central Colorado: Matuyama-Brunhes boundary: Journal of Geophysical Research, v. 105, no. B9, (2006) and Fridrich and Kirkham (2007). Deposits likely represent a Proterozoic metamorphic rocks and Tertiary volcanic rocks. Unit also properties of soils and landforms were used to correlate surficial deposits Golden, Colorado, Colorado School of Mines, Ph.D.