Regional Report: 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.

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