This release presents the GIS data (in GDB, shapefile, and e00 [coverage] formats) and metadata for a 1:24,000-scale geologic map of the Poncha Pass area in central Colorado. A cartographic version of the geologic map, including map unit descriptions, interpretative text, and accessory figures and tables, is being separately published as a U.S. Geological Survey Scientific Investigations Map (SIM). The map area is irregular in shape, covering all of one 7.5' quadrangle (Poncha Pass) and parts of five others (Mount Ouray, Maysville, Salida West, Salida East, and Wellsville). The map boundaries were drawn to cover all of the "Poncha mountain block", coincident with the approximately 15-kilometer-long northwestern end of the Sangre de Cristo Mountains. The map data convey the areal distribution of: (1) Proterozoic basement rocks forming the core of the Poncha mountain block, (2) overlying Tertiary volcanic rocks, (3) Miocene and younger basin-fill deposits, (4) Quaternary surficial glacial and alluvial deposits, and (5) faults and folds affecting all of the above units.

Fifty-three types of surficial geologic deposits and residual materials of Quaternary age are described in a pamphlet and located on a map of the greater Pueblo area, in part of the Front Range, in the Wet and Sangre de Cristo Mountains, and on the plains east of Colorado Springs and Pueblo. Deposits formed by landslides, wind, and glaciers, as well as colluvium, residuum, alluvium, and others are described in terms of predominant grain size, mineral or rock composition (e.g., gypsiferous, calcareous, granitic, andesitic), thickness, and other physical characteristics. Origins and ages of the deposits and geologic hazards related to them are noted. Many lines drawn between units on our map were placed by generalizing contacts on published maps. However, in 1997-1999 we mapped new boundaries as well. The map was projected to the UTM projection. This large map area extends from near Salida (on the west edge), eastward about 107 mi (172 km), and from Antero Reservoir and Woodland Park on the north edge to near Colorado City at the south edge (68 mi; 109 km).

This Data Release provides tabular and geospatial data digitized by the U.S. Geological Survey (USGS) from a U.S. Bureau of Mines (USBoM) report titled Mineral Investigation of Sangre de Cristo Wilderness Study Area, Alamosa, Custer, Fremont, Huerfano, and Saguache Counties, Colorado. The original preliminary paper report, numbered Mineral Land Assessment 65-83 (MLA 65-83; Ellis and others, 1983), presented the results of a mineral resource potential survey of areas in and around the Sangre de Cristo Range flanking the northeastern extent of San Luis Valley in south-central Colorado. Included in this Data Release are georeferenced scans of the regional plate maps, digitized sample site locations, analytical chemistry, and structural geologic data from MLA 65-83 in a modern and searchable geospatial database. In addition to the maps and associated point locations, the dataset contains 1,262 rows and 58 columns of contextual and numeric information in the main data table, as well as a table describing 97 samples excluded from the MLA report, a table of summary deposit information, a table of USBoM inventory data for the prepared and stored rock samples, and geospatial boundary data of the Sangre de Cristo Wilderness, Wilderness Study Area (WSA), and mineralized sampling areas. Prospecting, claiming, and some mining of largely polymetallic precious- and base-metal veins occurred in the Sangre de Cristo Range from the late 1800s through the early 1930s, with sporadic prospecting and some mining through the late 1980s (Ellis and others, 1983). Many of the vein networks are found along the western side of the mountains that are bounded by the Sangre de Cristo normal fault, a principal structure delineating a major segment of the Rio Grande rift. There also are mines along the crest and the northeast side of the range such as the Rita Alta copper mine. However, the locations of many claims, prospects, and mines were hand located on topographic and mine maps without modern spatial coordinate data and there were few analytical chemistry data available with properly associated geologic context. As a mandated component of the 1964 Wilderness Act, the USGS and USBoM were charged with identifying and assessing mineral resources in Federal lands known as Wilderness Study Areas (WSA; for example, Johnson and others, 1984). The Sangre de Cristo WSA included the mountainous areas from Poncha Pass in the north to the Blanca Peak area in the south. Most of the study area was ultimately designated as Wilderness in 1993. The unique sand dunes and associated watersheds on the western side of the central portion of the range, originally designated Great Sand Dunes National Monument in 1932, were redesignated as a National Park and Preserve in 2004. During the wilderness study, approximately 85 percent of the Sangre de Cristo WSA was covered by aerial photographic inspection and sites were visited by Ellis and others (1983) as access allowed. One thousand three hundred and ten (1,310) samples were collected and fire assayed for gold and silver as well as spectrographically analyzed for 40 other elements including copper, lead, molybdenum, tungsten, and uranium. Select samples were also analyzed for specific elements by various other state-of-the-art analytic methods of the time: copper, lead, and molybdenum by atomic absorption, tungsten by colorimetry, and uranium by fluorimetry. Integration of mapping, field characterization, mineralogical, and chemical data resulted in the identification of 18 more or less distinct mineralized areas. Sample locations (1,310) and a variety of enlargement maps (13) and mine maps (60) were compiled and integrated into the MLA 65-83 report along with extensive tabulation on paper with all data organized by mineralized area. During the late 1990's and 2000's the USGS completed extensive research in the Rio Grande Rift (for example, Hudson and Grauch, 2013) including the Sangre de Cristo Mountains and adjacent San Luis Valley. Much of the work focused on interpretation of new geophysical data and new geologic mapping as well as new analyses of mineralized areas and associated geologic structures. Overall, the absolute age, petrogenetic, and metallogenic affinities of the mineralized areas are poorly understood. However, some combination of magmatic, hydrothermal, structural, chemical, and fluid-related processes all contributed to the formation of the Sangre de Cristo mineral system. The digital data and information provided in this Data Release allows for public access to the information contained in the archived paper data record, report, and plates. This publication is useful in developing a better understanding of the geologic and tectonic framework, occurrences, and controls on mineralization and other Earth resources such as groundwater. References Cited Above: Ellis, C.E., Hannigan, B.J., and Thompson, J.R., 1983, Mineral Investigation of Sangre de Cristo Wilderness Study Area, Alamosa, Custer, Fremont, Huerfano, and Saguache Counties, Colorado: U.S. Bureau of Mines Mineral Land Assessment preliminary report MLA 65-83, 190 p., 2 plates, available at https://doi.org/10.5066/P98D3WXM. Hudson, M.R., and Grauch, V.J.S., 2013, Introduction, in Hudson, M.R., and Grauch, V.J.S., eds., New Perspectives on Rio Grande Rift Basins: From Tectonics to Groundwater: Geological Society of America Special Paper, v. 494, p. v-xii, https://doi.org/10.1130/SPE494. Johnson, B.R., Lindsey, D.A., Ellis, C.E., Hannigan, B.J., and Thompson, J.R., 1984, Mineral Resource Potential of the Sangre de Cristo Wilderness Study Area, South-central Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-1635-A and Pamphlet, 13 p., https://doi.org/10.3133/mf1635A.

The San Luis Valley and associated underlying basin of south-central Colorado and north-central New Mexico is the largest structural and hydrologic basin of the Rio Grande Rift and fluvial system. The surrounding San Juan and Sangre de Cristo Mountains reveal evidence of widespread volcanism and transtensional tectonism beginning in the Oligocene and continuing to the present, as seen in fault displacement of Pleistocene to Holocene deposits along the eastern basin-bounding Sangre de Cristo fault system and fault zones along the western margin of the basin. The San Luis basin can generally be subdivided into northern and southern basins at the structural and physiographic high terrain of the San Luis Hills in the center of the basin, proximal to the Colorado-New Mexico stateline. The northern San Luis Valley can be subdivided into two subbasins at approximately the latitude of the Great Sand Dunes and San Luis Lakes, where the endorheic northern subbasin surface and subsurface flow currently accumulate in a series of playa lakes. To the south of this playa region, the Rio Grande has captured basin hydrology into a through-going fluvial system cutting through the San Luis Hills, carving the Rio Grande gorge, and ultimately flowing into the Gulf of Mexico. This surficial geologic map of the northern San Luis Valley, paired with the Alamosa, CO 1:100,000-scale geologic map (U.S. Geological Survey Scientific Investigations Map 3342) provides new and compiled geologic mapping that characterizes basin deposits and locates the traces of active faults, with the goal to provide geospatial data for future investigations related to western North American neotectonics, Pleistocene paleoclimate, and related geomorphic processes. In addition, present natural and anthropogenic water bodies have been located and updated for hydrologic modeling and water-usage investigations.