The Ferguson Mountain Formation was named by Berge (1960) for limestones exposed at Ferguson Mountain in Sec. 16, T. 30 N., R. 69 E. The section named by Berge restricted the unit originally defined as the Ferguson Spring Formation by Steele (1960).

The Ferguson Mountain Formation is considered Lower Permian (upper Wolfcampian to lower Leonardian) in age. It is equivalent to the Riepe Spring Limestone plus Riepetown Sandstone and the lower part of the Arcturus Formation.

At the type section at Ferguson Mountain, the formation is alternating dark and light gray, massive and platy cherty limestone (Berge, 1960). The limestones are fine to medium-grained, contain both coraline and fusulinid coquinas, and are commonly silty. White, gray, and black chert nodules and thin beds are present in the limestone, as are thin interbeds of bituminous shale (Berge, 1960; Steele, 1960).

In the Dolly Varden Mountains the Ferguson Mountain is composed of thin-bedded, granular and bioclastic, dense, gray limestone in beds 6 inches to a few feet thick (Snow, 1964). The limestones are fusulinid-rich and are locally coquinites. The Ferguson Mountain is locally bleached and metamorphosed to a marble along Cretaceous quartz monzonite intrusives (Snow, 1964).

In the Wood Hills and Pequop Range area, the Ferguson Mountain Formation disconformably overlies the Ely Limestone and is composed of medium gray, aphanitic to coarse-grained bioclastic limestone with up to 80 percent of the limestone composed of fusulinids (Thorman, 1962). The limestone is silty and sandy, and all gradations from pure limestone to calcareous sandstone are present. Thin chert lenses are present throughout the unit, and the basal part of the Ferguson Mountain is composed of reddish-brown weathering siltstone to sandstone (Thorman, 1962).

In the Kingsley Range area, the Ferguson Mountain is massive, light brown to gray weathering, medium-grained argillaceous limestone with abundant bryozoans, fusulinids and corals. Light brown chert beds, nodules and stringers are scattered throughout the unit (Buckley, 1967).

In the Pilot and Leppy and southern Silver Island Ranges the Ferguson Mountain is part of an undivided Permian unit composed of thin to thick-bedded bioclastic medium-grained, dark gray limestone (O'Neill, 1968; Coats, 1985).

The Ferguson Mountain Formation is about 1,986 feet thick at the type section on Ferguson Mountain (Berge, 1960), about 1,200 feet in the Dolly Varden Mountains (Snow, 1964), 1,275 feet thick in the Kingsley Mountains (Buckley, 1967), about 275 feet thick in the Wood Hills-Pequop Range area (Thorman, 1962), and several hundred feet in an undivided and poorly exposed section about 2,550 feet thick in the Leppy and Pilot and southern Silver Island Ranges (Blue, 1960; Schaeffer and Anderson, 1960; O'Neill, 1968).

The Ferguson Mountain Formation is present at Ferguson Mountain near the southern end of the Goshute Range, in the Dolly Varden and Kingsley Mountains, Wood Hills and Pequop Range area, and in undivided sections in the Leppy, southern Silver Island and Pilot Ranges.

The Ferguson Mountain Formation represents shallow open marine deposition along the outer shelf.