The Highland Peak Formation was named the Highland Peak Limestone by Westgate and Knopf (1932) for exposures in T. 1 S., R. 66 E., and was restricted as currently used by Wheeler (1941).

The Highland Peak Formation contains trilobite faunas which are early Middle Cambrian to early Late Cambrian in age (Tschanz and Pampeyan, 1970). The Highland Peak Formation is equivalent to the lower portion of the Pole Canyon Limestone (Tschanz and Pampeyan, 1970)

The Highland Peak Formation has been broken into a lower portion with 6 members and an upper portion that is not broken into formal members (Merriam, 1964; Tschanz and Pampeyan, 1970). In general, the Highland Peak consists of alternating light and dark-gray to black, very fine to coarse-grained limestone, and massive to platy or laminated, white to dark-gray dolomite or dolomitic sandstone (Tschanz and Pampeyan, 1970).

Several authors have described the various members of the Highland Peak. The nomenclature of Merriam (1964) is used here and includes the Peasley, Burrows, Burnt Canyon, Step Ridge, Condor and Meadow Valley members in ascending order, which are in turn overlain by the undivided upper portion of the formation.

The Peasley Member is composed of dark gray to blue-gray, oolitic, detrital and algal limestone. The limestone is medium- grained, thickly bedded, and locally contains brachiopods (Merriam, 1964). It is commonly 100 to 150 feet thick.

The Burrows Member is composed of light to medium gray, thick- bedded to massive, medium to coarse-grained dolomite, and intertonguing fine-grained, light gray to white limestone with Girvanella algal nodules in the basal beds (Merriam, 1964). It is commonly 370 to 560 feet thick.

The Burnt Canyon Member is dark gray to black, thin bedded and laminated, fossiliferous, very fine grained limestone with reddish mottling and shale partings (Merriam, 1964: Tschanz and Pampeyan, 1970). The Burnt Canyon Member contains Girvanella algae and is locally cross-bedded in the upper 50 feet. It is commonly 160 to 300 feet thick.

The Step Ridge Member is dull gray, dense, lithographic, and mottled oolitic limestone. The limestone is commonly striped, contains forset crossbeds and is unfossiliferous (Merriam, 1964). It is commonly about 740 - 775 feet thick.

The Condor Member is composed of light gray silty saccharoidal dolomite, dark gray, fine-grained limestone, and thin-bedded and platy, fine-grained, dolomitic sandstone and siltstone which weather to a pink, gray or red-brown (Merriam, 1964). Black chert nodules and lenses up to 2 feet long and 8 inches thick are present throughout the member which is commonly 100 to 120 feet thick.

The Meadow Valley Member is medium to dark gray, fine to medium-grained, mottled limestone with pink argillaceous partings. Intraformational edgewise conglomerates are present in the Meadow Valley Member (Merriam, 1964). It is commonly 400 to 450 feet thick.

The upper portion of the Highland Peak Formation is composed of alternating light to dark gray, fine-grained, thick-bedded limestone and saccharoidal, gray mottled dolomite.

The Highland Peak Formation is about 4,500 feet thick in the Pioche district according to Merriam (1964).

The Highland Peak Formation is exposed in the eastern Wilson Creek Range, and forms a large portion of the Bristol and Highland Ranges as well as the Pioche Hills to the south of the evaluation area.

The depositional setting of the Highland Peak was a shallow restricted shelf, with lagoonal and local strandline environments. This is suggested by the abundance of Girvanella, trilobites and brachiopods, cross-bedded carbonates and calcareous siltstones and sandstones, and intraformational conglomerates.