Geologic map of the Granite 7.5’ quadrangle, Lake and Chaffee Counties, Colorado by Ralph R. Shroba, Karl S. Kellogg, and Theodore R. Brandt 2014 Scientific Investigations Map 3294 ABSTRACT: The geologic map of the Granite 7.5’ quadrangle, Lake and Chaffee Counties, Colorado portrays the geology in the upper Arkansas valley and along the lower flanks of the Sawatch Range and Mosquito Range near the town of Granite. The oldest rocks, exposed in the southern and eastern parts of the quadrangle, include gneiss and plutonic rocks of Paleoproterozoic age. These rocks are intruded by younger plutonic rocks of Mesoproterozoic age. Felsic hypabyssal dikes, plugs, and plutons, that range in age from Late Cretaceous or Paleocene to late Oligocene, locally intruded Proterozoic rocks. A small andesite lava flow of upper Oligocene age overlies Paleoproterozoic rock, just south of the Twin Lakes Reservoir. Gravelly fluvial and fan deposits of the Miocene and lower Pliocene(?) Dry Union Formation are preserved in the post-30 Ma upper Arkansas Valley graben, a northern extension of the Rio Grande rift. Mostly north-northwest-trending faults displace deposits of the Dry Union Formation and older rock units. Light detection and ranging (lidar) imagery suggests that two short faults, near the Arkansas River, may displace surficial deposits as young as middle Pleistocene. Surficial deposits of middle Pleistocene to Holocene age are widespread in the Granite quadrangle, particularly in the major valleys and on slope underlain by the Dry Union Formation. The main deposits are glacial outwash and post-glacial alluvium; mass-movement deposits transported by creep, debris flow, landsliding, and rockfall; till deposited during the Pinedale, Bull Lake, and pre-Bull Lake glaciations; rock-glacier deposits; and placer-tailings deposits formed by hydraulic mining and other mining methods used to concentrate native gold. Hydrologic and geologic processes locally affect use of the land and locally may be of concern regarding the stability of buildings and infrastructure, chiefly in low-lying areas along and near stream channels and locally in areas of moderate to steep slopes. Low-lying areas along major and minor streams are subject to periodic stream flooding. Mass- movement deposits and deposits of the Dry Union Formation that underlie moderate to steep slopes are locally subject to creep, debris-flow deposition, and landsliding. Proterozoic rocks that underlie steep slopes are locally subject to rockfall. Sand and gravel resources for construction and other uses in and near the Granite quadrangle are present in outwash-terrace deposits of middle and late Pleistocene age along the Arkansas River and along tributary streams in glaciated valleys. DISCLAIMERS: This database, identified as SIM3294, has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. 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 U.S. Geological Survey 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 contains copyrighted material as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. DATA FILES: The database can be downloaded via the Web from http://pubs.usgs.gov/sim/3294/. ArcInfo export files, ArcView shapefiles, and an ArcGIS geodatabase may be extracted from a zip-compressed file (SIM3294_GIS.zip). In addition, an Adobe Portable Document Format (PDF) file (SIM3294 _map.pdf, or SIM3294_map_hillshade) can be downloaded, from which paper copies may be printed. The database contact is: Theodore R. Brandt 303-236-1901 tbrandt@usgs.gov U.S. Geological Survey Box 25046, Mail Stop 980 Denver, CO 80225 The data were compiled form field mapping and interpretation of Lidar data, NAIP imagery, and aerial photographs. David J. Lidke (U.S. Geological Survey), Alan R. Nelson (U.S. Geological Survey), and Peter W. Birkeland (professor emeritus University of Colorado at Boulder) reviewed the geologic map and accompanying text. This geospatial database consists of ArcInfo export files (.e00), ArcView shapefiles, and ArcGIS geodatabase files contained in a zip archive. See the list below. Please refer to the file SIM3294.met for detailed metadata documentation for this geospatial database. List of files: 00ReadMe.txt SIM3294_pamphlet.pdf SIM3294_map.pdf SIM3294_map_hillshade.pdf (map with shaded relief base added) SIM3294.met granbasr.tif granbasr.tfw granhlsd.tif granhlsd.tfw granlihl.tif granlihl.tfw SIM3294_GIS.zip: e00 directory: grangeo.e00 grandike.e00 granpts.e00 granpta.e00 granage.e00 granhlsd.e00 granlihl.e00 wpgcmykg.shd.e00 geol_sfo.lin.e00 geoscamp2.mrk.e00 import.aml shapefiles directory: grangeo.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) polygon grangeol.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) line grandike.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) line granpts.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) point granpta.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) point granage.shp (.dbf/.prj/.sbn/.sbx/.shx.xml/.shx) point SIM3294_GIS.gdb directory (contains GIS data as geodatabase feature classes) HOW TO OBTAIN THE DIGITAL FILES: The digital files constituting the geologic map database of this report can be obtained via the Internet from the U.S. Geological Survey publications website. Go to the web page at http://pubs.usgs.gov/sim/3294/ and follow the directions to download the files. The main product is a Portable Document Format (.pdf) map, which requires Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com.