Kofa Mts (S.H. Mts), Yuma Co., Arizona, USA

A mountain range located 20 miles SE of Quartzsite and NE of the Castle Dome Moutnains. The alternate name of S.H. Mountains which allegedly stands for 'Stone House.'

This is an isolated mountainous area in the central part of Yuma County. They cover an area of approximately 200 square miles are are surrounded by broad, gently-aggraded plains that separate them from other detached mountains. The higher summits rise probably 2,000 feet above the surrounding plains.

These mountains are composed of extrusive igneous rocks which rest on an eroded surface of much older rocks. These older rocks are exposed in low foothills in the northern and southern parts of the mountainous area. The volcanic rocks are probably of tertiary and Quaternary age. The older rocks consist of metamorphosed sediments with associated pegmatites, thought to be of Precambrian age, intruded by granite and dike rocks of probable Mesozoic age. These rocks are intricated dissected into flat-topped mesas of small extent or into jagged spires and other fantastic erosional forms.

Mineralization is Au-Cu-Pb deposits that occur in certain fault zones. The bulk of these mountains consists of a gently Northward dipping block of Tertiary rhyolites, andesites and tuffs, capped by basalts, that rises to more than 4,000 feet above sea level, or 2,500 feet above the adjacent plains. Minor areas of schist, granite, and shales are exposed at the base of the volcanics. The granite is of interest since it contains copper deposits. Extensive faulting and fracturing have affected all of the rocks, particularly those of the pre-lava age.

References:
Jones, E.L., Jr. (1915), A Reconnaissance in the Kofa Mountains, Arizona, USGS Bull. 620: 151-164.

Wilson, E.D. (1933) Geology and Mineral Deposits of Southern Yuma County, Arizona. Arizona Bureau of Mines Bulletin 134: 106-109.

Walker, L.W. (1957), The geodes of Kofa, Nature: 50: 266-267.

Dale, V.B. (1959), Tungsten deposits of Yuma, Maricopa, Pinal, and Graham Counties, Arizona, U.S. Bureau of Mines Report of Investigation 5516.

Dahm, J.B., and Hankins, D.D. (1982) Preliminary geology of a portion of the southern Kofa Mountains, Yuma County, Arizona, in Frost, E.G., and Martin, D.L., eds., Mesozoic-Cenozoic tectonic evolution of the Colorado River region, California, Arizona, and Nevada - Anderson-Hamilton Volume: San Diego, Cordilleran Publishers, p. 459-469.

Hankins, D.D. (1984) Geologic map of a portion of the southern Kofa Mountains, Arizona: Arizona Bureau of Geology and Mineral Technology Miscellaneous Map MM-84-A, 1 sheet, scale 1:12,000.

Hankins, D.D. (1984) Geologic setting of precious metals mineralization, King of Arizona district, Kofa Mountains, Yuma County, Arizona: San Diego, San Diego State University, M.S. thesis, 135 p., 1 sheet, scale 1:12,000.

Charlton, D.W., Copeland, D.J., Reaugh, L.W., and Westall, N.D. (1985) Gold mineralization in low angle faults, Verdstone property, Kofa Mountains, Arizona [abs.]: Geological Society of America Abstracts with Programs: 17(6): 348.

Blair, Gerry (1992), The Rockhound's Guide to Arizona: Helena, MT, Falcon Press: 157.

Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 236, 349, 364.

Ferguson, C.A., and Skotnicki, S.J. (1996) Geology of the northern Kofa Mountains (Owl Head and northern third of the Kofa Butte 7.5' quadrangles), Yuma and La Paz Counties, Arizona: Arizona Geological Survey Open-File Report 96-03, 22 p., 2 sheets, scale 1:24,000.

Skotnicki, S.J., and Ferguson, C.A. (1996) Geology of the Cholla Tank and northern third of the Hoodoo Well quadrangles), northern Kofa Mountains, Yuma and La Paz Counties, Arizona: Arizona Geological Survey Open-File Report 96-24, 11 p., 1 sheets, scale 1:24,000.