An area of approximately 73 square kilometers has been mapped in the Toiyabe Range of central Nevada. The geology consists primarily of Lower Cambrian through Lower Devonian shales and limestones and their apparent metamorphosed equivalents, slates, phyllites, and marbles. Deposition of these rocks occurred in the transition zone of the Cordilleran Geosyncline. A deep water shelf slope appears to be the depositional environment for much of the sediments, although there is evidence for periods of uplift during which more bioclastic limestones were deposited. The Toiyabe Ridge, a topographic high during the Upper Silurian and Devonian, was the source of the bioclastic debris found in the McMonnigal Limestone. Several periods of structural deformation have occurred in the area, including the Devonian Antler Orogeny, Mesozoic plutonism, Tertiary volcanism, and Pleistocene block faulting. A portion of the Roberts Mountains Thrust (associated with the Antler Orogeny) is present in the north where the Ordovician Valmy Formation overlies the Devonian-Silurian McMonnigal Formation. The Kingston Canyon Thrust (a smaller, local feature) is also believed to have occurred during the Antler Orogeny. A felsite pluton in the northwest may have been formed during the Late Mesozoic. The tuff breccias on the east side of the Range are Oligocene in age.