The eight tracts surveyed, identified as extensions A through H, lie along the flanks of the Bighorn Mountains in Big Horn, Johnson, and Sheridan Counties, Wyo.; they border the primitive area studied by the same agencies in 1970 (Kiilsgaard and others, 1972). The areas of the present study total approximately 133,000 acres (54,000 hectares), which, added to the 136,000 acres (55,000 hectares) of the officially designated Cloud Peak Primitive Area and to the 94,000 contiguous acres (38,000 hectares) that were studied in 1970, make a grand total of about 363,000 acres (147,000 hectares). About 450 unpatented lode and placer claims have been recorded in the area, but nothing has been produced from these claims. The eight extensions studied in 1972, like the original area studied in 1970, are underlain almost entirely by igneous and metamorphic rocks of Precambrian age, except for extension D. This area is underlain mostly by sedimentary rocks of Paleozoic age that dip gently westward into the Bighorn Basin. The area of extension A is fringed by the same types of Paleozoic rocks, but, there, they dip steeply eastward into the Powder River Basin. Glacial moraines fan out in all directions from the central highland of the Bighorn Mountains, covering bedrock in the flanking areas. Geological, geochemical, and geophysical investigations, mine and prospect examinations, and analyses of samples of stream sediments and bedrock were all used in making a mineral appraisal of the study areas. The results of this work are the same as those obtained in 1970 from the Cloud Peak Primitive Area and vicinity: they show that the eight newly proposed extensions to the area are without economically significant mineral resources. These extensions, in common with the rest of the Bighorn Mountains area studied for wildnerness evaluation, are also without evidence for potential resources for coal, oil, gas, geothermal energy, or commercial quantities of nonmetallic minerals.
