OF-15-02 Geologic Map of the Castor Gulch Quadrangle, Moffat County, Colorado


The purpose of this report is to describe the geology, geologic resources and geologic hazards of this 7.5-minute quadrangle located in north-western Colorado. CGS staff geologist Peter E. Barkmann, along with William Curtiss, Christopher J. Carroll, Daniel R. Hosler, Nathan T. Rogers, Zachary D. Logan, and Michael J. Zawaski completed the field work on this project during the summer and fall of 2014. Digital ZIP download. OF-15-02D

Location (excerpted from USGS Open-File Report 79-820, 1979)

The Castor Gulch quadrangle is located in southeastern Moffat County in northwestern Colorado, approximately 1 mile (2 km) south of the town of Craig via Colorado Highway 13 (also known as Colorado Highway 789), and approximately 43 miles (69 km) southwest of the town of Steamboat Springs via Colorado Highway 13 and U.S. Highway 40. The town of Craig South Highlands is in the north-central part of the quadrangle. A few scattered ranches occur throughout the remainder of the quadrangle.

Previous geologic mapping

The first geologic description of the general area in which the Castor Gulch quadrangle is located was reported by Emmons (1877) as part of a survey of the Fortieth Parallel. The decision to build a railroad into the region stimulated several investigations of coal between 1886 and 1905, including papers by Hewett (1889), Hills (1893), and Storrs (1902). Fenneman and Gale (1906) conducted geologic studies of the Yampa Coal Field and included a description of the geology and coal occurrence in the Castor Gulch quadrangle in their report. Hancock (1925) includes the entire area within the Castor Gulch quadrangle and is the most comprehensive work on the area. Tweto (1976) compiled a generalized regional geologic map which included this quadrangle.