Bear Butte, South Dakota
Location: 44.5N, 103.4W
Elevation: 4,422 feet (1,348 m)
Bear Butte is a laccolith located on the Black Hills, an area of uplifted Precambrian on the Wyoming - South Dakota state line. Bear Butte is made of magma that never reached the surface to generate an eruption. The magma intruded to a shallow level and then stopped, cooled, crystallized, and solidified. Erosion then stripped the overlying layers of rock away. Bear Butte is at the east end of a linear belt of volcanic centers that continues westward about 60 miles (100 km) to Devils Tower. The rock is called a trachyte based on its mineral composition, which includes alkali feldspar with small amounts of biotite, hornblende, and pyroxene. Bear Butte rises 1,253 feet (382 m) above the surrounding plain. Photo by Steve Mattox, October 1995.
Sources of Information:
Green, J. and Short, N.M., 1971, Volcanic landforms and surface features a photographic atlas and glossary: Springer Verlag, New York, 519 p.
Karner, F.R., and Halvorson, D.L., 1987, The Devils Tower, Bear Lodge Mountains, Cenozoic igneous complex, in Beus, S.S., ed., Centennial Field Guide Volume 2 Rocky Mountain Section of the Geological Society of America, p. 161-164.