stripes
Devils Tower is a vertical pinnacle of rock rising for nearly 200 m above talus covered slopes. The base is some 250 m in diameter. Spectacular polygonal columns extend continuously from the base to the summit, tapering slightly upwards. The rock is a porphyritic phonolite with phenocrysts of alkali feldspar and augite zoned to aegirine in a groundmass of orthoclase, aegirine, probable nepheline, analcime, zeolite and accessories. The area was established as the first National Monument of the U. S. in 1906.
HILL, D.J., IZETT, G.A. and NAESER, C.W. 1975. Early Tertiary fission track ages of sphene from Devils Tower and Missouri Buttes, Black Hills, northeastern Wyoming. Abstracts with Programs, Geological Society of America, 7: 613-4.
LISENBEE, A. KARNER, F., FASHBAUGH, E., HALVORSON, D., O'TOOLE, F., WHITE, S., WILKINSON, M. and KIRCHENER, J. 1981. Geology of the Tertiary intrusive province of the Northern Black Hills, South Dakota and Wyoming. In F.J. Rich (Ed.). Geology of the Black Hills, South Dakota and Wyoming. American Geological Institute, Field Trip Guidebook: 33-105.
ROBINSON, C.S. 1956. Geology of Devils Tower National Monument, Wyoming. Bulletin, United States Geological Survey, 1021-I: 289-302