Discover the Geology of Vedauwoo

I-80 travelers between Laramie and Cheyenne will likely notice mounds of rocks to the north of the interstate. The rocks have been eroded into fanciful shapes, and some are precariously balanced, making them appear to be moments away from toppling over.

Vedauwoo is a popular destination for climbers, hikers, and mountain bikers. It is a unique geologic area in the Laramie Mountains, with 1.4-billion-year-old Sherman Granite jutting out of the rolling hills at an 8,000-foot elevation. The outcrops in and around Vedauwoo are almost entirely made up of rocks of the Sherman batholith, which is a large mass of intrusive igneous rock that crystallized from magma deep within the earth’s crust.

There are three major rock units in the Sherman batholith: Sherman Granite, Lincoln granite, and porphyritic granite. Minor dark-colored mafic rocks also occur throughout the batholith. The unique outcrops at Vedauwoo are the product of weathering and erosion of the Sherman batholith. East-northeast trending fractures in the area provide planes of weakness for erosional forces to exploit, resulting in the ridges and fins of granite that are common in the area. Erosion of the Sherman Granite produces a residual deposit of very coarse-grained gravel, called grus.

Southeast of Vedauwoo is the fascinating geologic feature called the Gangplank, which is a thin, gently sloping remnant of sedimentary rock that allowed a smooth ascent to the Rocky Mountains by the Union Pacific Railroad and later the Lincoln Highway.

Additional information about the Vedauwoo Recreation Area can be found on the U.S. Forest Service website and in the Roadside Geology of Wyoming.

►References

Frost, C.D., Frost, B.R., Chamberlain, K.R., and Edwards, B.R., 1999, Petrogenesis of the 1.43 Ga Sherman batholith, SE Wyoming, USA–A reduced, rapakivi-type anorogenic granite: Journal of Petrology, v. 40, no. 12, p. 1,771-1,802.

Contact:
Christina George, christina.george@wyo.gov