OF-01-01 Geologic Map of the Castle Rock Gulch Quadrangle, Chaffee and Park Counties, Colorado


The Castle Rock Gulch Quadrangle is located in Chaffee and Park Counties. The map shows the distribution of various rock types and their configuration and provides information about potential resources and hazards. Includes cross-section, map unit correlation, shaded-relief map with geology overlay, booklet of extended descriptions of map units, economic geology and selected references. 31 pages, 1 color plate (1:24,000). Digital PDF download. OF-01-01D

From the Author’s Notes:

The Castle Rock Gulch quadrangle is located in the east-central part of Chaffee County and the southwestern part of Park County in the central part of the Mosquito Range about 21 km north of Salida, Colorado and 10 km east of Buena Vista, Colorado. U.S. Highways 285 and 24 pass through the northwestern part of the quadrangle. The map area includes rugged terrain and steep canyons along the western border and northwestern part of the quadrangle and high rolling hills in the southern and central parts of the quadrangle. Kaufman Ridge and Bassam Ridge are prominent topographic features that trend southeast and northwest in the map area. Elevations range from about 8,600 to 10,800 ft.

The oldest rocks in the quadrangle are Proterozoic igneous and metamorphic rocks that are overlain unconformably by Paleozoic sedimentary rocks, Tertiary volcanic and sedimentary rocks, and Quaternary slope-wash, talus, landslide, and stream deposits. A large sill of probable Laramide age (Late Cretaceous or Paleocene) intruded Pennsylvanian sedimentary rocks in the northwestern part of the map area. Steep faults offset Proterozoic and Paleozoic rocks. Large- and medium-scale anticlines and synclines deform Paleozoic rocks. Mid-Tertiary volcanic rocks and associated tuffaceous sediment were deposited in a prominent paleovalley that trends from southwest to northeast across the quadrangle. Tertiary volcanic rocks in the map area are mainly intermediate and silicic welded tuff and air-fall tuff, and Tertiary sedimentary deposits are poorly consolidated, tuffaceous silt, sand, and gravel.