By: J. J. Anderson and P. D. Rowley
The western half of the Circleville quadrangle is in the southeastern Tushar Mountains, the eastern half in the Sevier River valley. These areas are in the High Plateaus subprovince which is structurally transitional between the block-faulted Basin and Range Province to the west and the more stable Colorado Plateaus of which it is a part.
The Marysvale volcanic field, one of the largest eruptive piles in the western United States, straddles the High Plateaus and extends into the Basin and Range Province. The quadrangle contains part of one of the most voluminous and extensive accumulations of this volcanic field, the Mount Dutton Formation. It consists of rock erupted from a series of clustered stratovolcanos distributed in a crudely defined east-trending zone across the southern Tushar Mountains. The formation extends from just east and southeast of the area of this map, in the southwestern Sevier Plateau, to the northern Black Mountains, about 30 miles to the west. Because of repetition by numerous high-angle dip-slip faults and because of the resistant nature of the rocks, a significant part of this volcanic vent complex is well exposed in the quadrangle, particularly on the imposing east-facing scarp west of Oak and Cottonwood Basins in the northwestern part of the quadrangle and in road cuts along highway U.S. 89 in Circleville Canyon. The Osiris Tuff, a regional ash-flow tuff interbedded high in the Mount Dutton section, and. minor accumulations of volcanic rocks of local origin that post-date the Mount Dutton Formation also occur in the quadrangle.
Pages: 5 p.
Plates: 2 pl.
Location: Beaver County, Garfield County, and Piute County
Media Type: Paper Map