More than 22,000 feet of Precambrian to Upper Devonian rocks crop out in the Specter Range Quadrangle. These rocks have been divided into fourteen formations; from the oldest to the youngest they are the Johnnie Formation, Stirling Quartzite, Wood Canyon Formation, Carrara Formation, Bonanza King Formation, Dunderberg Shale, Nopah Formation (restricted), Lower Pogonip Group undifferentiated (which includes the Goodwin Limestone and Ninemile Formation), Antelope Valley Limestone, Eureka Quartzite, Ely Springs Dolomite, Undifferentiated Silurian rocks, Nevada Formation, and Devils Gate Limestone. The four oldest formations, Precambrian to lower Middle Cambrian, are composed of clastic rocks; quartzite, siltstone, and shale with thin beds of limestone and dolomite. From lowe Middle Cambrian through Upper Devonian, the rocks are mainly limestone and dolomite with thin beds of quartzite and quartz sandstone. The formational names recognized during this study are probably applicable over a wide area in south-central Nevada where in large part the stratigraphy is poorly known.

Four formations are of particular interest. The Antelope Valley Limestone is mapped for the first time in this part of Nevada and its lithologic and time equivalence with the type section is demonstrated. The Goodwin Limestone and Ninemile Formation are also tentatively identified for the first time. The age of the Nevada Formation has been established as Lower Devonian (Spirifer kobehana Zone) and Middle Devonian (Stringocephalus Zone); equivalent to the rocks of the type section in the Eureka district.