The Sherman Mountains are erosional remnants rising above the general level of the surface of the Laramie Range. Their flat-topped character resulted from beveling during an ancient erosion cycle. The bedrock here is granite, a crystalline rock made up of pink feldspar, glassy quartz, black mica, and hornblende, which originated deep in the earth's crust over a billion years ago. The peculiar rock forms of the Sherman Mountains are controlled by three sets of joints, or planes of weakness, cutting the granite and dividing it into large blocks. Weathering has rounded off corners and enlarged joint planes, resulting in irregular block rock masses, many of which are capped by balance rocks.