The Atokan Series in east-central and southern Nevada and western Utah consists mostly of a repetitive sequence of carbonate rocks belonging to the Ely Group (Ely Limestone of several workers). The many vertical changes in local stratigraphic sections and general lack of persistent thin lithostratigraphic markers attest to deposition conducive to numerous and complex lateral variations. Moreover, the probability that species of fusulinids used for time-stratigraphic determinations are facies-restricted and the widespread deformation preclude precise correlation of narrowly defined time-stratigraphic units within the more broadly defined Atokan Series. Petrographic analysis, however, permitted recognition of nine limestone types that have been linked in a conceptual model elating environmental energy, relative depth, and biologic distribution: type 1, spiculiferous fine-grained limestone; type 2, fine-grained limestone and skeletal calcarenitic limestone; type 3, mud-supported calcarenitic limestone with pelletoid grains absent or not abundant; type 4, grain-supported calcarenitic limestone with pelletoid grains absent or subordinate; type 5, fine-grained and medium-grained calcarenite; type 6, coarse calcarenite and calcirudite; type 7, mud-supported and grain-supported pelletoid calcarenitic limestone; type 8, Komia limestone; type 9, Donezella limestone.

Rock type 1 and most varieties of type 2 probably represent deepest water deposition and, with type 9, they are interpreted as having originated under the lowest energy conditions. Rock type 6 formed under the highest energy conditions of deposition. Chaetetes-bearing units are common, and Chaetetes is believed to have flourished primarily in areas of deposition of fine-grained limestone and calcarenitic limestone, the rocks which constitute most of the "matrices" in Chaetetes-bearing units.

Most of the foregoing characteristics apply to Atokan carbonate sequences in other parts of the eastern Great Basin.