The McColley Canyon Formation, Lower Devonian of central Nevada, is divisible into three members, the Kobeh, Bartine, and Coils Creek in ascending order. The two lower members have been mapped in the Sulphur Springs Range, Roberts Mountains, Lone Mountain, and Table Mountain. The Coils Creek Member has been mapped in the latter three ranges, but its stratigraphic position is occupied by the lower Union Mountain Formation in the Sulphur Springs Range. This correlation indicates a late Early Devonian age for the lower part of the Union Mountain Formation.
The Coils Creek Member bears the Elythyna fauna in its upper part, which, though small, is distinct trom the Eurekasfirifer pinvonensis Zone fauna below and the Leptathyris circula above.