The Condor Canyon Formation was named for exposures in Condor Canyon in Secs. 22, 23, 24, 26 and 27, T. 1 S., R. 68 E. in the Pioche Hills (Cook, 1965).

The Condor Canyon Formation is Lower Miocene in age and has been radiometrically dated at 21 to 24 Ma (Ekren and others, 1977). The Bauers Tuff Member is 21.3 +/- 0.5 Ma in the Golden Gate Range (Armstrong, 1970).

The Condor Canyon Formation has been divided into two moderately to strongly welded members, the lower Swett and upper Bauers ignimbrites. Both are quartz-free, and similar in color and texture but vary in mineralogy, particularly phenocryst content, and distribution (Ekren and others, 1977). Color in these vitric tuffs is typically a reddish or purple gray which gives a bluish appearance from a distance, and texture is typified by "running pumice" where pumice fragments have been strung out by flowage and welding so that they resemble flow laminae. Both members commonly have a black vitrophyric base, which in the case of the Bauers Member, contains large hollow bubble-like spherulites known as lithophysae (Cook, 1965).

The Bauers Member is commonly more uniform in thickness, and from 58 feet to 257 feet, while thicknesses from 30 to 450 feet are typical in the Swett Member (Cook, 1965). The main distinguishing feature however, is phenocryst percentage and lithology. The Swett Member has about 5 percent phenocrysts made up of 80 to 95 percent potassium feldspar and 15 percent biotite. The Bauers Member contains 10 to 20 percent phenocrysts with 50 to 70 percent potassum feldspar, 30 to 40 percent alkali feldspar, 3 to 7 percent biotite, and about 1 percent orthopyroxene (Ekren and others, 1977).

The Condor Canyon Formation is 376 feet thick at its type locality, and varies from about 350 to 650 feet in thickness in northeastern Lincoln County (Ekren and others, 1977; Cook, 1965).

The Condor Canyon has an extensive distribution both to the south and east of the evaluation area. It is present in the Pioche Hills, Wilson Creek, Golden Gate, Seaman, and Fortification Ranges area within the study area.