Geologic Map of the Fraser 7.5-minute Quadrangle, Grand County, Colorado Pamphlet to accompany Scientific Investigations Map 3130 U.S. Department of the Interior U.S. Geological Survey COVER: View to the southeast, from high gravel-capped hill near the town of Winter Park, looking toward snow- clad peaks along the Continental Divide east of Berthoud Pass. High peak on the far left is James Peak, 13,294 ft, (4,052 m). In foreground, the dense forest is composed of conifers and aspen, and is growing in soils formed in surficial deposits and weathered bedrock. Photograph by R.R. Shroba, September 26, 2006. Geologic Map of the Fraser 7.5-minute Quadrangle, Grand County, Colorado By Ralph R. Shroba, Bruce Bryant, Karl S. Kellogg, Paul K. Theobald, and Theodore R. Brandt Pamphlet to accompany Scientific Investigations Map 3130 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2010 For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://www.store usgs.. gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Shroba, R.R., Bryant, Bruce, Kellogg, K.S., Theobald, P.K., and Brandt, T.R., 2010, Geologic map of the Fraser 7.5-minute quadrangle, Grand County, Colorado: U.S. Geological Survey Scientific Investigations Map 3130, scale 1:24,000, 1 sheet, 26 p. pamphlet. [Available at URL http://pubs.usgs.gov/sim/3130]. iii Contents Introduction.....................................................................................................................................................1 Description of Map Units ..............................................................................................................................5 Surficial Deposits ..................................................................................................................................5 Artificial Fill Deposits...................................................................................................................5 Alluvial Deposits...........................................................................................................................5 Alluvial and Mass-Movement Deposits ...................................................................................8 Mass-Movement Deposits .........................................................................................................9 Glacial Deposits .........................................................................................................................10 Bedrock Units ......................................................................................................................................11 Post-Laramide Sedimentary and Volcanic Rocks ................................................................11 Pre-Laramide Sedimentary Rocks ..........................................................................................12 Proterozoic Rocks ......................................................................................................................12 Eolian Silt Contributions to the Troublesome Formation in the Fraser Basin .....................................14 Structural Setting of the Fraser 7.5-minute Quadrangle .......................................................................16 Geologic History of the Fraser 7.5-minute Quadrangle .........................................................................16 Proterozoic History .............................................................................................................................16 Paleozoic through Laramide History ...............................................................................................17 Post-Laramide Cenozoic History ......................................................................................................17 Acknowledgments .......................................................................................................................................21 References Cited..........................................................................................................................................21 Figures 1. Index of 7.5- and 15-minute quadrangles referred to in this report ..............................3 2. Regional geologic setting of parts of the Front and Gore Ranges and adjacent basins ..............................................................................................................4 3. Index of geologic mapping in figure 2 ................................................................................5 4. Plot of mean particle size and degree of sorting (standard deviation of the mean particle size) of silty sandstone, siltstone, and clayey siltstone collected from the Troublesome Formation near Fraser, Colorado .............................15 Tables 1. Particle-size analyses of silty sandstone, siltstone, and clayey siltstone collected from the Troublesome Formation near Fraser, Colorado ......................................2 2. Approximate height, in meters, of top of gravelly stream alluvium (Qg and QNg) above the Fraser River and its major tributaries: Saint Louis Creek and Ranch Creek in the Fraser 7.5-minute quadrangle ........................13 3. Mean annual precipitation near Kremmling, Granby, and Fraser, Colorado ....................15 4. Mean January and July temperatures near Fraser, Colorado, and estimated mean January and July temperatures near the Mary Jane site, about 9 km southeast of Fraser .....................................................................................................................20 iv Conversion Factors Multiply By To obtain Length centimeter (cm) 0.3937 inch (in.) meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) square kilometers (km2) 0.386 square miles (mi2) Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F=(1.8×°C)+32 Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C=(°F-32)/1.8 Altitude, as used in this report, refers to distance above the vertical datum. v Divisions of Quaternary, Neogene, and Paleogene time used in this report Period or Subperiod Epoch Age Holocene 0–11.5 ka Quaternary late 11.5–132 ka Pleistocene middle 132–788 ka early 788 ka–1.81 Ma Neogene Pliocene 1.81–5.33 Ma Miocene 5.33–23.0 Ma Paleogene Oligocene 23.0–33.9 Ma Eocene 33.9–55.8 Ma Paleocene 55.8–65.5 Ma Ages of time boundaries are those of the U.S. Geological Survey Geologic Names Committee (2007) except those for the late-middle Pleistocene and middle-early Pleistocene boundaries, which are those of Richmond and Fullerton (1986a). Ages are expressed in ka for kilo-annum (thousand years) and Ma for mega-annum (million years). North American land mammal ages used in this report Land Mammal Age Age Hemphillian 4.7–8.9 Ma Clarendonian 8.9–11.6 Ma Arikareean 19–29 Ma Ages of time boundaries are those of Woodburne and Swisher (1995). Geologic Map of the Fraser 7.5-minute Quadrangle, Grand County, Colorado By Ralph R. Shroba, Bruce Bryant, Karl S. Kellogg, Paul K. Theobald, and Theodore R. Brandt Introduction on Stratigraphic Nomenclature, 1983), whereas the other map units (“bedrock units”) are informal or formal lithostrati- graphic or informal lithodemic units. For these reasons, subdi- The geology of the Fraser 7.5-minute quadrangle was visions of allostratigraphic or lithodemic units use time terms compiled from previous and new mapping. Theobald mapped much of the southern one-third of the quadrangle during “late” and “early” as applied to surficial units or Proterozoic 1959–1963. Many of the geologic units and geologic features crystalline units, but we use position terms “upper” and observed by Theobald along old logging roads and some of the “lower” where applied to lithostratigraphic units. aqueduct cuts are no longer visible, due chiefly to the depo- Age assignments for surficial deposits within the map sition of colluvium and regeneration of dense forest cover. area are based chiefly on relative heights above present stream Materials available from Theobald’s work in the Fraser quad- channels, the relative degree of modification of their original rangle included a preliminary geologic map of the southern depositional morphology, and degree of soil development and one-third of the quadrangle, field notes, and field sheets. None clast weathering. of his petrographic information, rock samples, or map-unit The mapped distribution of surficial map units is based descriptions was available to the other co-authors. primarily on interpretation of 1:40,000-scale, color-infrared Bryant made a reconnaissance geologic map of the aerial photographs taken in 1988 (National Aerial Photogra- northern two-thirds of the Fraser quadrangle during 1974 as phy Program (NAPP), http://egsc.usgs.gov/isb/pubs/booklets/