The Edgemont Formation was named for exposures along Edgemont Canyon in Sec. 29, T. 44 N, R. 51 E., on the western flank of the Bull Run Mountains within the Bull Run Quadrangle (Decker, 1962).

The Edgemont Formation is Lower Cambrian in age based upon identification of a deformed trilobite (Decker, 1962).

The Edgemont Formation is a blue-gray to brown schistose and slaty lithology which gradationally overlies the Prospect Mountain Quartzite and is overlain by the Porter Peak Limestone at the type section in the Bull Run Quadrangle (Decker, 1962; Coats, 1985). The lower portion of the formation is a schistose quartzite while the upper portion is commonly a limestone. In the Bull Run Mountains the Edgemont Formation is composed of siltstone, mudstone and limestone (Clark and others, 1985).

At the type section, the Edgemont Formation is about 700 feet thick, and it is about 1,100 feet thick in other exposures within the Bull Run Mountains (Clark and others, 1985).

The Edgemont is present in the Bull Run Mountains, and may be equivalent to schists in the Rowland Quadrangle in northern Elko County.

The depositional setting for the Edgemont Formation is very poorly understood. Clark and others (1985) suggest that the Edgemont Formation represents initial miogeoclinal subsidence following the fluvial deposition of the Prospect Mountain Quartzite over the Precambrian rift sediments of the McCoy Creek Group. Like the Porter Peak, the Edgemont probably represents relatively shallow marine shelf to upper slope deposition.