Title: Geologic Map of the Fort Collins 30'×60' Quadrangle, Larimer and Jackson Counties, Colorado, and Albany and Laramie Counties, Wyoming By Jeremiah B. Workman, James C. Cole, Ralph R. Shroba, Karl S. Kellogg, and Wayne R. Premo U.S. Geological Survey Scientific Investigations Report 3399 U.S. Geological Survey data release https://doi.org/10.5066/F7G44PHV ABSTRACT The rocks and landforms of the Fort Collins 30'×60' 1:100,000-scale U.S. Geological Survey quadrangle reveals a particularly complete record of geologic history in the northern Front Range of Colorado. The Proterozoic basement rocks exposed in the core of the range preserve evidence of Paleoproterozoic marine sedimentation, volcanism, and regional soft-sediment deformation, followed by regional folding and gradational metamorphism. Mesoproterozoic time was marked by intrusion of the Berthoud Plutonic Suite into crust that was structurally neutral or moderately extending in an east-northeast direction. Evidence of the late Paleozoic Anasazi uplift (Ancestral Rocky Mountains uplift) within the quadrangle is recorded by removal of Permian and older sediments and deposition of proximal Pennsylvanian and Permian strata unconformably onto the exhumed Proterozoic basement rocks. The Phanerozoic sediments indicate a steady progression of fluvial, eolian, and lacustrine environments throughout most of the Mesozoic Era which was a time of relatively slow sediment accumulation. Early Cretaceous time was marked by incursion of the Cretaceous Western Interior Seaway, a shallow-water marine embayment that persisted throughout the latter part of the Mesozoic Era. Sedimentation rates increased significantly in the latter part of this period during down-warping related to distant crustal loading by thrusting along the western continental margin. With onset of the Laramide orogeny in latest Cretaceous time, mountain building resumed in this region. This deformation placed Proterozoic rock over Cretaceous and Paleocene strata along the western margin of the Front Range and Medicine Bow Mountains. Post-Laramide time was marked by a prolonged period of weathering, erosion, and planation of the basement-rock surface, extending perhaps into late Oligocene or early Miocene time. Erosion on the eastern slope of the Front Range in late Paleogene to early Neogene time produced a broad, rolling surface surrounding residual highlands and east-trending fluvial channels filled with coarse, boulder gravel. Significant global cooling during the Pliocene led to glaciation during the Quaternary. In the Rocky Mountain region, renewed uplift allowed erosion to accentuate the topographic relief across the high mountains of the map area and established the elevations necessary to trigger accumulation of persistent snow and ice. Mountain glaciers advanced and retreated during at least three glacial-interglacial cycles during the middle and late Pleistocene in this area. Erosion continues to this day on the High Plains east of the mountain front, and progressive incision of the drainage is recorded by at least five major gravel-clad terrace and pediment surfaces along the major fluvial channels that connect to the South Platte River system. DISCLAIMERS Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. This database, identified as SIM 3399, has been approved for release by the U.S. Geological Survey (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 (USGS), 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 any 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. ------------------------------------------------------------------------------- FILES: The map, pamphlet, and its accompanying text files can be downloaded via the Web at http://doi.org/10.3133/sim3399. REPORT FILES sim3399_Readme.txt sim3399.pdf sim3399_sheet.pdf sim3399_sheet_georeferenced.pdf ------------------------------------------------------------------------------- ScienceBase GIS data release for this report can be down loaded at: https://doi.org/10.5066/F7G44PHV GIS FILES INCLUDED IN THIS REPORT sim3399_GIS.gdb.zip GeologicMap ContactsAndfaults CrossSectionLines DataSourcePolys GeologicLines IsoValueLines MapAreaPoly MapUnitPoints MapUnitPolys OrientationPoints sim3399_shapefiles.zip ContactsAndfaults.shp (cpg./dbf./prj./sbn./shp.xml./shx./) CrossSectionLines.shp (cpg./dbf./prj./sbn./shp.xml./shx./) DataSourcePolys.shp (cpg./dbf./prj./sbn./shp.xml./shx./) GeologicLines.shp (cpg./dbf./prj./sbn./shp.xml./shx./) IsoValueLines.shp (cpg./dbf./prj./sbn./shp.xml./shx./) MapAreaPoly.shp (cpg./dbf./prj./sbn./shp.xml./shx./) MapUnitPoints.shp (cpg./dbf./prj./sbn./shp.xml./shx./) MapUnitPolys.shp (cpg./dbf./prj./sbn./shp.xml./shx./) OrientationPoints.shp (cpg./dbf./prj./sbn./shp.xml./shx./) sim3399.mxd ------------------------------------------------------------------------------- HOW TO OBTAIN THE DIGITAL FILES: The text files that accompany this report can be obtained at http://doi.org/10.3133/sim3399/ and follow the directions to download the files. Suggested citation: Workman, J.B., Cole, J.C., Shroba, R.R., Kellogg, K.S., and Premo, W.R., 2017, Geologic map of the Fort Collins 30'×60' quadrangle, Larimer and Jackson Counties, Colorado, and Albany and Laramie Counties, Wyoming: U.S. Geological Survey Scientific Investigations Map 3399, pamphlet 83 p.,scale 1:100,000, http://dx.doi.org/10.3133/sim3399/. ------------------------ The ScienceBase 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 ScienceBase web page at http://doi.org/10.5066/F7G44PHV Suggested citation: Workman, J.B., Cole, J.C., Shroba, R.R., Kellogg, K.S., and Premo, W.R., 2017, Data release for geologic map of the Fort Collins 30'×60' quadrangle, Larimer and Jackson Counties, Colorado, and Albany and Laramie Counties, Wyoming: U.S. Geological Survey data release, http://dx.doi.org/10.5066/F7G44PHV/. ------------------------ The manuscript product is a Portable Document Format (.pdf) report, 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 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.