The historic South Pass-Atlantic City and Lewiston districts are characterized by abundant small lode and placer deposits with additional potential for large-tonnage, low-grade mineralization and small undiscovered high-grade deposits. This area is a greenstone belt that forms a synclinorium of metamorphosed sedimentary, volcanic, and plutonic rocks intruded by granitic plutons. Gold mineralization occurs mainly in foliation-parallel shear zones and is associated with quartz, sulfides, carbonates, and related wallrock alterations. An estimate by Hausel (1989) suggests that as much as 334,000 ounces of gold were mined from the South Pass-Atlantic City district.

Placer and paleoplacer gold deposits are widespread in the vicinity of the greenstone belt. The Oregon Buttes-Dickie Springs paleoplacers are a few miles south of the South Pass-Atlantic City district. Love, Antweiller, and Mosier (1978) described these paleoplacers as hosting as much as 28.5 million ounces of placer gold.