About 10,000 ft. of Ordovician through Permian rocks crop out within the Arrow Canyon Range. Cambrian black dolomite and argillaceous limestone also are exposed. Ordovician rocks include about 2400 ft. in the Pogonip Group, about 100 ft. of Eureka Quartzite, and about 400 ft. of Ely Springs Dolomite. The Silurian Laketown Dolomite thins southward from 400 to about 250 ft. because of pre-Devonian erosion. Devonian rocks are approximately 2000 ft. thick. The Piute Formation, about 300 ft. thick, consists of buff dolomite and contains Acrospirifer kobehana at the base and a Stringocephalus sp. biostrome at the top. The bench-forming, buff dolomite Moapa Formation, 300 ft. thick, which succeeds the Stringocephalus biostrome is overlain by about 1100 ft. of dark, cliff-forming limestone of the Arrow Canyon Formation which includes several prominent interbedded sandstone layers. The uppermost Devonian formation, the Crystal Pass Limestone, is about 250 ft. thick and is disconformably succeeded by black limestone of the Mississippian Monte Cristo Group. The Monte Cristo Group is about 1500 ft. thick, and all of the subunits named by Hewett excepting the Arrowhead Limestone are recognized. Pennsylvanian and Permian rocks, referred to the Bird Spring Group, include about 3500 ft. of rock assigned to 5 formations. The basal formation consists of about 80 ft. of limestone resting on a basal sandstone. This unit is succeeded by a detrital formation assigned to the Indian Springs Formation. Rhipidomella nevadensis occurs at the base of the overlying cyclic limestone of Pennsylvanian and Permian age. This formation is overlain by 300 ft. of limestone and shale which are, in turn, succeeded by a Permian limestone formation in the Bird Spring Group. Comparison with sections on the SE. and NW. and computation of approximate rates of sedimentation suggest that a hinge-line between the Paleozoic shelf and miogeosyncline may have shifted back and forth across this area during Ordovician through Permian time. The apparent hinge-line may have resulted from pre-Devonian erosion on the SE., local basin development on the NW. during Devonian time, and introduction of detrital rocks from the NW. during the Mississippian and from the SE. during the Pennsylvanian and Permian. Rates of sedimentation appear to have been relatively uniform in the Arrow Canyon Range during the Paleozoic.

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