Stratigraphy of Middle Ordovician quartz arenites and related rocks is traced from central Nevada to central Utah, and correlations with northern Utah rocks are suggested. Following accumulation of thick, fossiliferous Pogonip carbonate rocks, miogeosynclinal regressive Kanosh argillites and the Watson Ranch tongue of the Swan Peak quartzite were deposited in west-central Utah and along the southwest flank of the Tooele arch, a Middle Ordovician emergent element west of Provo, synchronous with Chazyan Swan Peak argillite and quartzite deposition in northern Utah. After subsequent accumulation of the Crystal Peak dolomite, the basal regressive phase of the Eureka quartzite was spread westward from central Utah, culminating in the fossiliferous undaform edge Copenhagen form tion in central Nevada. Continued emergence caused deep erosion in part of north-central Nevada and moderate to slight erosion elsewhere.

Transgressive Trentonian Eureka quartzites, with several distinct members of approximate time-rock value, were deposited in thickness over much of Nevada and western Utah, and probably into central Utah. At least sporadically developed in northern Utah, the Eureka quartzite may be thickly developed there, represented by rocks now considered as type Swan Peak and close correlatives. Continued transgression forming latest Trentonian and early Cincinnatian carbonates was interrupted, probably by widespread emergence, so that Richmondian dolomites lie on Eureka quartzite and other Middle Ordovician and Lower Ordovician rocks.