Geologic Map and Sections of the Holy Cross Quadrangle, Eagle, Lake, Pitkin,and Summit Counties, Colorado by Ogden Tweto Digital Edition and GIS Database by Theodore R. Brandt, released 2013 U.S. Geological Survey Miscellaneous Investigations Series Map I-830, ABSTRACT This map was first published as a printed edition in 1974. The geologic data have now been captured digitally and are presented here along with images of the printed map sheets. The map encompasses the area of four 7.5-minute quadrangles between 39º15' and 39º 30'N and 106º15' and 106º30'W in the Sawatch and Gore mountain ranges, and upper part of the Arkansas River drainage in central Colorado. The Holy Cross geologic map depicts in detail the complex geology at the north end of the Sawatch Range on the west at its junction with south end of the Gore Range on the east. The ranges are separated in the southern part of the map area by the upper reaches of the Arkansas River, and in the northeast part by the narrow valley of the upper Eagle River. Sixty map units and numerous individual beds and thin units within the principal map units are shown. Paleoproterozoic and Mesoproterozoic metamorphic rocks are the principal rocks of the Sawatch Range. In the Gore Range, lower and upper Paleozoic sedimentary rocks rest unconformably on the Precambrian metamorphic rocks. Paleozoic rocks that range in age from Upper Cambrian though Middle Pennsylvanian support the Gore Range along the eastern quarter of the map. The sequence includes a basal quartzite overlain by interbedded, shale, dolomite, quartzite, and sandstone. The Leadville Dolomite, below the dark shale, is the host rock for the ore deposits at Leadville and the neighboring lead-zinc-silver districts. A wide range of Miocene to Cretaceous intrusive rocks dip east off the Sawatch Range. The Dry Union Formation of Pliocene and Miocene age fills the valley of the Arkansas River and is covered by Quaternary alluvium and glacial sediment. Glacial deposits of Bull Lake, Pinedale, and neoglacial age are present in many of the mountain valleys. The geologic structure of the quadrangle is complex in geometry and time with a distinct structural and geographic break along the west front of the Gore Range in the eastern quarter of the quadrangle. In general, Paleozoic strata intruded by Tertiary and Cretaceous irregular linear plutons and sills of the Gore Range are tilted east from the Sawatch Range. These rocks are broken by major normal faults in a complex pattern commonly associated with Paleocene? and Cretaceous intrusive porphyries. In the Sawatch Range, two large Precambrian igneous complexes are separated by a broad shear zone of Precambrian age that extends northwest across the quadrangle and beneath Paleozoic rocks of the Gore Range. Down-to-valley normal faults define the margins of the Arkansas and upper Eagle River valleys. The Leadville, Sugarloaf, and St. Kevin districts have produced significant amounts of silver. The Homestake mine at the head of West Tennessee Creek produced silver and lead from veins bearing siderite and barite. Scattered veins in shear zones along Homestake Creek are mainly argentiferous galena veins; some are quartz and copper. Veins at Holy Cross City produced gold. Other veins in the area have produced gold, silver, and minor amounts of copper. DISCLAIMERS This database, identified as I-830, 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/imap/830/. ArcInfo export files, ArcView shapefiles, and an ArcGIS geodatabase may be extracted from a zip-compressed file (I-830_GIS.zip). In addition, an Adobe Portable Document Format (PDF) file (I-830_map.pdf) can be downloaded, from which paper copies may be printed. CONTACT 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 CONTENTS 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 I-830.met for detailed metadata documentation for this geospatial database. List of files: 00ReadMe.txt I-830_map.pdf I-830_xsec.pdf I-830.met I-830textonly.doc datafiles I-830_GIS.zip: hcbasr.aux hcbasr.tfw hcbasr.tif I-830.mxd I-830.pmf e00.zip directory: hcgeo.e00 hcqr.e00 hcxc.e00 hcpts.e00 hcpta.e00 hcptd.e00 hcptf.e00 hcptps.e00 hchlsd.e00 hcbasr.tif hcbasr.tfw wpgcmykg.shd.e00 geol_sfo.lin.e00 geoscamp2.mrk.e00 import.aml Shapefiles.zip directory: hcgeo.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) polygon hcgeol.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) line hcqr.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) line hcxc.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) line hcpts.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) point hcpta.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) point hcptd.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) point hcptf.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) point hcptps.shp (.dbf/.prj/.sbn/.sbx/.shp/.shx/.xml) point I-830_GIS.gdb directory (contains GIS data as geodatabase feature classes) hcgeo hcgeol hcqr hcxc hcpts hcpta hcptd hcptf hcptps 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/imap/i-830 and follow the directions to download the files. The main product is a Portable Document Format (.pdf) map, which requires Adobe Acrobat for viewing, and from which paper copies may be printed. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com. ArcReader may be downloaded free of charge from http://www.esri.com/software/arcgis/arcreader/download.htm for viewing additional files included in this report.