OF-99-03 Geologic Map of the Gribbles Park Quadrangle, Park and Fremont Counties, Colorado


The Gribbles Park Quadrangle is located in the southern Mosquito Range. Gold, base metal mineralization, industrial minerals, and construction materials occur in the area. Includes cross section, map unit correlation, shaded-relief map with geology overlay, booklet of extended descriptions of map units, previous studies, present studies, geologic setting, structure, volcanic activity, and references. 21 pages. 1 color plate (1:24,000). Digital PDF download. OF-99-03D

From the Author’s Notes:

The Gribbles Park quadrangle is located in southern Park County and northwestern Fremont County in the southern part of the Mosquito Range. This quadrangle includes an upland of rolling hills and grass land and sparse ponderosa forest at high elevation northeast of Salida, Colorado.

The oldest rocks exposed in the quadrangle are Proterozoic metamorphic and igneous rocks, which are overlain unconformably by Paleozoic sedimentary rocks, Tertiary volcanic and sedimentary rocks, and Quaternary alluvial and colluvial deposits. The Late Cretaceous Whitehorn Granodiorite intruded Paleozoic sedimentary rocks. Steep faults offset Proterozoic and Paleozoic rocks. The Weston-Pleasant Valley fault trends northward through the quadrangle; this fault was probably an active fault in part of late Paleozoic time and after Late Paleozoic time. Paleozoic rocks are folded into broad homoclinal sequences or are folded into moderate-scale anticlines and synclines. Late Cretaceous plutonic rocks and Tertiary volcanic and sedimentary rocks are cut by few faults. Tertiary volcanic rocks and volcanogenic sedimentary rocks cover Proterozoic and Paleozoic rocks over much of the quadrangle. Volcanic rocks are composed mainly of silicic welded tuff and air-fall tuff, but in the eastern part of the map area basaltic Tertiary flows cap mesas locally. Tertiary volcanogenic sedimentary rocks were deposited during eruption of silicic tuff, and were coeval with welded tuff and ash-flow tuff deposits. Tertiary units are truncated by Pleistocene pediment deposits, and alluvial and colluvial deposits occur in most drainages.