Wyoming State Geological Survey releases new geologic map of Gas Hills area

This is an outcrop of the Eocene Wind River Formation in the southern Gas Hills in eastern Fremont County, consisting of mildly radioactive, highly oxidized arkosic sandstone and conglomerate. Uranium was first discovered about a mile southwest of this location in September 1953. The Puddle Springs member of the Wind River Formation is the host rock of uranium deposits that have produced more than 100 million pounds of uranium oxide concentrate (yellowcake) since mining began in 1954. Photo h/t Robert Gregory, WSGS]

The Wyoming State Geological Survey (WSGS) has published two new preliminary bedrock geologic maps under its StateMap Program. The 1:24,000-scale mapping projects focus on areas in central and southeastern Wyoming.

“Geologic maps are fundamental building blocks of geologic analysis,” says WSGS Director, Dr. Erin Campbell. “These two maps were created in support of studies on uranium exploration and mineralization trends within Wyoming.”

The Gas Hills map examines structure and uranium host rocks as there are more than two dozen historic uranium mines and several developing uranium mining projects in the area. The project better constrains the age of the base of the middle Eocene Wagon Bed Formation, identifies minor previously unmapped structures, and includes mapped landslides, not only along the Beaver Divide (also known as Beaver Rim) escarpment but also the flanks of the Dutton Basin Anticline. Additionally, the new mapping complements the Ervay Basin SW and Ervay Basin mapping projects completed in 2016.

“The Gas Hills uranium district is one of the most important in the state of Wyoming,” says lead project geologist, Robert Gregory. “Detailed mapping of the Gas Hills quadrangle has helped further our understanding of the relationships between the various rock units, particularly the uranium-bearing formations, and the structures that affected the deposition of uranium ore.”

The WSGS received funding for the mapping projects through the U.S. National Cooperative Geologic Mapping Program managed by the U.S. Geological Survey. With the completion of the two new maps, the WSGS has produced 30 geologic maps at 1:24,000 scale and 75 geologic maps at 1:100,000 scale as part of the StateMap Program.

“The StateMap Program provides funds that allow the Survey to maximize existing time and resources,” says Campbell. “With the help of the StateMap-funded contractors and sample analyses, we are able to produce more maps and gather more data.”

New mapping projects under development and scheduled to be released next year are bedrock geologic maps at 1:24,000 scale of the Garden Gulch quadrangle in Carbon County, the Lankin Dome quadrangle in Fremont and Natrona counties, and the Horatio Rock quadrangle in Albany and Carbon counties.

For more information about WSGS geology mapping, including available maps, visit the agency’s website.

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