OF-12-07 Geologic Map of the Marmot Peak Quadrangle, Chaffee and Park Counties, Colorado


The purpose of this publication is to describe the geologic setting, mineral and water resources, and geologic hazards of this 7.5-minute quadrangle located south of Fairplay in central Colorado. Consulting geologists Karen Houck, Jonathan Funk, and Bob Kirkham, staff geologist Chris Carroll, and field assistant Alyssa Heberton-Morimoto completed the field work on this project during the summer of 2007. Digital ZIP download. OF-12-07D

From the Author’s Notes:

The Marmot Peak 7.5-minute quadrangle is located on the western margin of the South Park Basin in central Colorado. Marmot Peak, in the west-central part of the quadrangle, is about 20 miles south-southwest of Fairplay and about seven miles north-northeast of Buena Vista. U.S. Highway 285 is just east of the quadrangle boundary. The northeastern half of the quadrangle is in the South Platte River drainage basin, and the southwestern half is in the Arkansas River drainage basin. The Park/Chaffee county line follows the drainage divide. The highest points in the quadrangle are West Buffalo Peak (13326 feet) and East Buffalo Peak (13,300 feet) in the northwestern part of the map area. Elevations decrease to the south and east, and the lowest elevations are in the southwestern part of the quadrangle (about 8,300 feet) near the Arkansas River Valley. Most of the quadrangle lies within the Pike and San Isabel national forests, which are administered by the USDA Forest Service. The Buffalo Peaks Wilderness Area, established in 1980, extends into the northwestern part of the quadrangle. The southeastern part of the quadrangle contains a parcel of land administered by the Colorado State Land Board.

On the USGS topographic base map of the Marmot Peak quadrangle, the labels for Spring Creek and Pony Creek are reversed. According to the Geographic Names Information System, the northern creek is Pony Creek and the southern creek is Spring Creek. The corrected names are shown on Plate 1. The oldest rocks exposed in the Marmot Peak quadrangle are Proterozoic in age and consist primarily of granodiorite, granite, gneiss, and migmatite. These rocks crop out along the western and southern margins of the quadrangle. Generally east-dipping Paleozoic rocks overlie the Proterozoic rocks and include, from oldest to youngest, the Cambrian Sawatch Sandstone and Dotsero Formation; the Ordovician Manitou Dolomite, Harding Sandstone, and Fremont Dolomite; the Devonian Parting Sandstone and Dyer Dolomite; the Mississippian Leadville Limestone; the Pennsylvanian Belden and Minturn formations, and the Pennsylvanian to Permian (?) Maroon Formation. Tertiary igneous rocks include dikes in the southwestern part of the quadrangle and the volcanic rocks comprising the Buffalo Peaks in the northwestern part. Quaternary surficial deposits of alluvium, colluvium, and talus occur throughout the quadrangle. Landslide deposits, solifluction deposits, and glacial till occur around the Buffalo Peaks, and extensive alluvial-fan deposits occur in Pony Park. Faults in the quadrangle have a variety of orientations and reflect a complex structural history with numerous episodes of deformation. Major faults include the Long Park, Buffalo Creek, Trout Creek, Pony Park, Salt Creek, 435, Brush Park, and Chubb Park faults.