Title: Surficial Geology of the Northern San Luis Valley, Saguache, Fremont, Custer, Alamosa, Rio Grande, Conejos, and Costilla Counties, Colorado By Chester A. Ruleman and Theodore R. Brandt 2021 U.S. Geological Survey Scientific Investigations Map 3475 Data release available at https://doi.org/10.5066/P9PUTQYK ABSTRACT: 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 state line. 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, Colo. 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. DISCLAIMERS: Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty, expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. Although this information product, for the most part, is in the public domain, it also may contain copyrighted material as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. ---------------------------------------------------------------------------- FILES: The map sheets can be downloaded via the Web from the U.S. Geological Survey publications website at https://doi.org/10.3133/sim3475. The map sheets are in an Adobe Portable Document Format (PDF) (sim3475_sheet1.pdf and sim3475_sheet2.pdf) from which paper copies may be printed. The geospatial PDF (sim3475_sheet1_georeferenced.pdf) has preserved the original layering of the map and, if a PDF reader like Adobe Acrobat Pro is used, these can be individually toggled "on" and "off" to change the visible information in the file. This capability as well as the "Measuring Tool" with the "Objct Data" and "Geospatial Location" tools will function if the file has been downloaded (functionality can't be guaranteed if opened in an internet browser). Note that the basemap layer is above the geologic unit polygon layer and effectively blocks the polygon layer. Because of this ordering, the basemap layer needs to be turned "off" when the "Object Data Tool" is used. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com. MAP FILES: sim3475_sheet1.pdf sim3475_sheet1_georeferenced.pdf sim3475_sheet1_hillshade_base.pdf sim3475_sheet2.pdf 00ReadMe.txt ---------------------------------------------------------------------------- The GIS database for this report is located at and can be downloaded via the Web from ScienceBase at https://doi.org/10.5066/P9PUTQYK HOW TO OBTAIN THE DIGITAL MAP FILES: The map sheets can be obtained via the Internet from the U.S. Geological Survey publications website. Go to the web page at https://doi.org/10.3133/sim3475 and follow the directions to download the files. PUBLICATION REFERENCE: Ruleman, C.A., and Brandt, T.R., 2021, Surficial geology of the northern San Luis Valley, Saguache, Fremont, Custer, Alamosa, Rio Grande, Conejos, and Costilla Counties, Colorado: U.S. Geological Survey Scientific Investigations Map 3475, 2 sheets, scale 1:75,000, https://doi.org/10.3133/sim3475. HOW TO OBTAIN THE DIGITAL GIS FILES: The digital GIS files constituting the geologic map database of this report can be obtained from the U.S. Geological Survey via the Internet from ScienceBase: ScienceBase link: https://doi.org/10.5066/P9PUTQYK DATA RELEASE REFERENCE: Ruleman, C.A., and Brandt, T.R., 2021, Data release for the surficial geology of the northern San Luis Valley, Saguache, Fremont, Custer, Alamosa, Rio Grande, Conejos, and Costilla Counties, Colorado: U.S. Geological Survey Scientific Investigations Map 3475, 2 sheets, scale 1:75,000, https://doi.org/10.5066/P9PUTQYK. ArcReader may be downloaded free of charge from http://www.esri.com/software/arcgis/arcreader/download for viewing additional files included in this report. This map is offered as an online-only, digital publication. Users should be aware that, because of differences in rendering processes and pixel resolution, some slight distortion of scale may occur when viewing it on a computer screen or when printing it on an electronic plotter, even when it is viewed or printed at its intended publication scale.