Study of exposed uppermost Precambrian and Lower Cambrian strata in southern and east-central Nevada and intervening areas indicates that the Johnnie Formation of southern Nevada and the McCoy Creek Group (restricted) are correlative. In detail, the uppermost units of both sequences, the Rainstorm Member of the Johnnie Formation and the Osceola Argillite (and the equivalent unit G) of the McCoy Creek Group, arc lithologically similar and also considered correlative. Both are characterized by pale-red or purplish-medium-gray siltstone with abundant bedding-surface markings, and both contain scarce to abundant amounts of evenly or lenlicularly laminated limestone or silty limestone. Both units are lithologically unique in their respective areas of occurrence, and both are known to be widely distributed. Several thousand feet of dominantly detrital rocks occur above the Johnnie Formation in southern Nevada and the McCoy Creek Group in east-central Nevada. These detrital rocks consist of quartzite and siltstone in southern Nevada (the Stirling Quartzite, Wood Canyon Formation, and Zabriskie Quartzite) and dominantly quartzite (the Prospect Mountain Quartzite) in cast-central Nevada. Study in areas between southern and east-central Nevada indicates that the Stirling, Wood Canyon, and Zabriskie Formations change facies to the north and become lithologically similar to one another. The Prospect Mountain Quartzite of east-central Nevada is believed to be the final result of the facies change. It is equivalent to the combined Stirling, Wood Canyon, and Zabriskie of southern Nevada.
