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At the request of the Bureau of Land Management, the U.S. Geological Survey and U.S. Bureau of Mines studied the Indian Pass (CDCA-355) Wilderness Study Area and the Picacho Peak (CDCA355 A) Wilderness Study Area in eastern Imperial County, Calif. Mineral surveys were conducted on 33,640 acres of the Indian Pass Wilderness Study Area and 5,450 acres of the Picacho Peak Wilderness Study Area. Field work for this report was carried out between 1982 and 1985. Within the collective area of the two study areas, there were 344 active mining claims in 1982. The prospects visited and sampled within and adjacent to the Indian Pass Wilderness Study Area have no identified resources. However, a tract having high resource potential for gold was delineated in the southwestern part of the Indian Pass Wilderness Study Area. This tract has been the site of much exploration activity for gold since 1983. Other tracts located within the Indian Pass Wilderness Study Area have moderate resource potential for gold and silver, moderate potential for tungsten, and low potential for gold, lead, zinc, and copper. The prospects sampled within and adjacent to the Picacho Peak Wilderness Study Area have no identified resources. Tracts having high resource potential for gold were delineated in the north-central part of the Picacho Peak Wilderness Study Area. Other tracts within the Picacho Peak Wilderness Study Area have low potential for undiscovered gold, lead, zinc, and copper resources. Character and Setting The Indian Pass and Picacho Peak Wilderness Study Areas occupy the southeast end of the Chocolate Mountains approximately 25 mi north-northwest of Yuma, Ariz., in easternmost Imperial County, Calif. (fig. 1). The relief is about 1,800 ft with rugged hills, steep-walled arroyos, and broad sandy washes. The study areas are underlain by rocks ranging in age from Proterozoic(?) and Mesozoic to Quaternary (see appendix 1 for geologic time chart). The structurally lowest rocks in the study areas are Proterozoic(?) and Mesozoic gneiss and Jurassic(?) supracrustal and granitic rocks that have been superposed over the late Mesozoic Orocopia Schist along the Late Cretaceous Chocolate Mountains thrust. Weakly to moderately metamorphosed Jurassic(?) supracrustal and granitic rocks are also juxtaposed against the gneiss and Orocopia Schist along younger normal faults. At Peter Kane Mountain, the Orocopia Schist was intruded and thermally remetamorphosed by a pluton at about 21-26 million years before the present (Ma). Block faulting in Oligocene time was followed by silicic volcanism, which continued into early Miocene time. Regional extension followed soon after the cessation of volcanism. Conglomerate marks the erosion of the volcanic field. Latest Tertiary(?) and Quaternary conglomerate, sandstone, and siltstone unconformably overlie the older rocks and structures. California's earliest mineral production (worked in 1779-81 by Spanish miners) was from placer gold deposits in the region just south of the study areas. Lode gold deposits at the Picacho mine, approximately 5 mi east-southeast of the Picacho Peak Wilderness Study Area, and the Cargo Muchacho district, about 10 mi south of the study areas (fig. 1), were discovered in the late 19th century. Identified Resources The 37 prospects visited and sampled during this study contained no identified resources. However, our sampling and the recent drilling program by Gold Fields Mining Corporation provide strong evidence that gold resources exist in the Indian Pass and Picacho Peak Wilderness Study Areas. There has been no mineral production from the study areas.

Mineral resources of the Indian Pass and Picacho Peak Wilderness Study Areas, Imperial County, California