NEWS RELEASE: The WSGS Publishes 2 New Geologic Maps from the Central Laramie Mountains

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Wyoming State Geological Survey

Nov. 4, 2021


Media Contact:
Tammy Mack
(307) 766-2286 x239


The WSGS Publishes 2 New Geologic Maps from the Central Laramie Mountains

The Wyoming State Geological Survey (WSGS) published bedrock geologic maps of the Poe Mountain and Guide Rock 1:24,000-scale quadrangles, located in the Laramie Mountains in southeast Wyoming. These maps represent decades of work and significant collaboration between multiple universities, the U.S. Geological Survey, and the WSGS.

“The maps were 30 years in the making,” says coauthor Dr. B. Ronald Frost, Emeritus professor at the University of Wyoming (UW) Department of Geology and Geophysics. “They were going to be published by the U.S. Geological Survey, but stalled for many years after the death of coauthor Dr. George Snyder.”

Frost then approached the WSGS about publishing them.

“These two maps are an excellent contribution to the understanding of geology of Wyoming,” says WSGS Director and State Geologist, Dr. Erin Campbell. “They reflect great collaborative effort by geologists from various agencies, and the outcome is comprehensive mapping of an area with complex intrusive relationships.”

Central to these two maps, which straddle the Albany-Platte county border, is the Laramie Anorthosite Complex (LAC). The 1.4-billion-year-old LAC contains numerous groups of igneous rocks, especially anorthosite (a somewhat rare intrusive igneous rock characterized by more than 90 percent plagioclase feldspar). The maps highlight the layering of the Poe Mountain anorthosite, which extends for about 5 miles across both quadrangles. The maps also provide details on the intrusive relations between the Poe Mountain anorthosite and the later Sybille intrusion.

“The maps show how the contact between the Sybille intrusion and the country rock is steep in the west and gradually becomes shallower to the east. As the contact becomes shallower, the Sybille intrusion begins to host large rafts of the country rock,” Frost says. “The Poe Mountain quadrangle shows how the Red Mountain pluton and associated dikes intrude both the Poe Mountain anorthosite and the Sybille intrusion.”

In addition to Frost and Snyder, students from the UW Geology and Geophysics Department, and Dr. Donald H. Lindsley and students from the Department of Geosciences at Stony Brook University in New York authored the maps.

The maps are available as free downloads and as hard copies for purchase from the WSGS sales site.