GEOLOGIC MAP OF THE CIRCLEVILLE QUADRANGLE, BEAVER, PIUTE, IRON, AND GARFIELD COUNTIES, UTAH By John J. Anderson and Peter D. Rowley U.S. Geological Survey UTAH GEOLOGICAL AND MINERAL SURVEY a division of UTAH DEPARTMENT OF NATURAL RESOURCES MAP82 1986 STATE OF UTAH Norman H. Bangerter, Governor DEPARTMENT OF NATURAL RESOURCES Dee C. Hansen, Executive Director UTAH GEOLOGICAL AND MINERAL SURVEY Genevieve Atwood, Director BOARD James H. Gardner, Chairman ................................................. University of Utah Kenneth R. Poulson . Brush Wellman, Inc. Jo Brandt .................................................................... Public-at-Large Robert L. Haffner ......................................... American Gilsonite/Chevron Resources Samuel C. Quigley ....................................................... Tower Resources, Inc. Lawrence Reaveley . Reaveley Engineers & Associates Ralph A. Miles, Director, Division of State Lands .................................. ex officio member UGMS EDITORIAL AND ILLUSTRATIONS STAFF J. Stringfellow ........................................................................ Editor Leigh M. MacManus, Carolyn M. Olsen ............................................. Editorial Staff Kent D. Brown, James W. Parker, Patricia H. Speranza ................................ Cartographers UTAH GEOLOGICAL AND MINERAL SURVEY 606 Black Hawk Way Salt Lake City, Utah 84108-1280 THE UTAH GEOLOGICAL AND MINERAL SURVEY is one of eight divisions in the Utah Department of Natural Resources. The UGMS inventories the geologic resources of Utah (including metallic, nonmetallic, energy, and ground-water sources); identifies the state's geologic and topographic hazards (including seismic, landslide, mudflow, lake level fluctuations, rockfalls, adverse soil conditions, high groundwater); maps geology and studies the rock formations and their structural habitat; provides and disseminates educational materials concerning the geology of Utah; and provides information to decisionmakers at local, state, and federal levels. THE UGMS is organized into five programs. Administration provides support to the programs. The Econom­ ic Geology Program undertakes studies to map mining districts, to monitor the brines of the Great Salt Lake, to identify coal, geothermal, uranium, petroleum and industrial minerals resources, and to develop computerized resource data bases. The Applied Geology Program responds to requests from local and state governmental entities for site investigations of critical facilities, documents, responds to and seeks to understand geologic hazards, and compiles geologic hazards information. The Geologic Mapping Program maps the bedrock and surficial geology of the state at a regional scale by county and at a more detailed scale by quadrangle. THE INFORMATION PROGRAM distributes publications, and answers inquiries from the public and man­ ages the UGMS library. The UGMS Library is open to the public and contains many reference works on Utah geology and many unpublished documents about Utah geology by UGMS staff and others. The UGMS has begun several computer data bases with information on mineral and energy resources, geologic hazards, and bibliographic references. Most files are not available by direct access but can be obtained through the library. THE UGMS PUBLISHES the results of its investigations in the form of maps, reports, and compilations of data that are accessible to the public. For future information on UGMS publications, contact the UGMS Sales Office, 606 Black Hawk Way, Salt Lake City, Utah 84108-1280. GEOLOGIC MAP OF THE CIRCLEVILLE QUADRANGLE, BEAVER, PIUTE, IRON, AND GARFIELD COUNTIES, UTAH By John J. Anderson 1 and Peter D. Rowley 2 U.S. Geological Survey INTRODUCTION logic mapping has been done to the north of the mapped area by Callaghan and Parker (1962) and Cunningham and others (1979, 1983), to the west by Anderson (1986), to The western half of the Circleville quadrangle is in the the east by Rowley (1968), and to the south by Anderson southeastern Tushar Mountains, the eastern half in the (1965). Sevier River ("Long") valley. These areas are in the High Plateaus subprovince which is structurally transitional be­ STRATIGRAPHY tween the block-faulted Basin and Range Province to the west and the more stable Colorado Plateaus of which it is a Rocks exposed in the Circleville quadrangle total nearly part. 5,000 feet 0524 m) in thickness and range in age from Oli­ The Marysvale volcanic field, one of the largest eruptive gocene to Holocene. Most belong to central-vent stratovol­ piles in the western United States, straddles the High Pla­ canos of the Oligocene and Miocene Mount Dutton Forma­ teaus and extends into the Basin and Range Province. The tion; rock types such as lava flows, autoclastic flow breccia, quadrangle contains part of one of the most voluminous and volcanic mudflow breccia make up the bulk of this and extensive accumulations of this volcanic field, the unit. Other volcanic units are intertongued with and overlie Mount Dutton Formation. It consists of rock erupted from the Mount Dutton Formation. The Osiris Tuff is a regional a series of clustered stratovolcanos distributed in a crudely ash-flow tuff high in the Mount Dutton section. Overlying defined east-trending zone (Rowley and others, 1978) units include the mafic lava flows of Circleville Mountain across the southern Tushar Mountains. The formation ex­ and the mafic gravels of Gunsight Flat, local units that tends from just east and southeast of the area of this map, have not been formally named. During late Tertiary and in the southwestern Sevier Plateau, to the northern Black Quaternary block faulting activity, down thrown blocks lo­ Mountains, about 30 miles (48 km) to the west. Because of cally filled with elastic sediments derived from nearby up­ repetition by numerous high-angle dip-slip faults and be­ thrown blocks. Circle Valley is the largest of these grabens, cause of the resistant nature of the rocks, a significant part and it was partially filled with poorly consolidated upper of this volcanic vent complex is well exposed in the Tertiary sedimentary strata of the Sevier River Formation quadrangle, particularly on the imposing east-facing scarp and by unconsolidated Quaternary sediments assigned to west of Oak and Cottonwood Basins in the northwestern several informal units. part of the quadrangle and in road cuts along highway U.S. 89 in Circleville Canyon. The Osiris Tuff, a regional ash­ TERTIARY SYSTEM flow tuff interbedded high in the Mount Dutton section, Mount Dutton Formation and. minor accumulations of volcanic rocks of local origin that post-date the Mount Dutton Formation also occur in The most commonly exposed rocks in the Circleville the quadrangle. General discussions of the geology in and quadrangle are volcanic units of intermediate (dacite to near the Circleville quadrangle may be found in Rowley (1968), Anderson and others (197 5), Rowley and Ander­ 1 Currently: Department of Geology, Kent State University, Kent, Ohio son (1975), Rowley and others (1978, 1979), Shawe and 44242 Rowley (1978), and Steven and others (1978, 1979). Geo- 2 Geologist, U.S. Geological Survey, Denver, Colorado 80225 2 Utah Geological and Mineral Survey andesite) composition interbedded locally with felsic and mostly sparse small phenocrysts of hornblende in a mi­ mafic volcanic rock and tuffaceous sandstone. These rocks crocrystalline and largely devitrified glass groundmass. The belong to the Mount Dutton Formation of Oligocene and predominant mudflow breccia is characterized by sub­ Miocene age. In accordance with the concepts of Parsons rounded to angular clasts of volcanic rock identical to that (1965, 1969) and Smedes and Prostka (1973), the forma­ of the vent facies, most commonly suspended in a muddy tion has been subdivided into a vent facies and an alluvial to sandy matrix. The ratio of clasts to matrix varies greatly facies, both the products of a series of stratovolcanos trend­ in different mudflows, and the thickness of the flows ing more-or-less eastward across what today comprises the ranges from a foot to several tens of feet. A largely fluvial southernmost Tushar Mountains. Vent facies rocks, the conglomerate, and the tuffaceous sandstone of partly fluvial near-source products of the stratovolcanos, consist of lava and partly eolian origin, consist almost exclusively of flows and autoclastic flow breccia and subordinate volcanic reworked volcanic detritus, much of which doubtlessly was mudflow breccia, conglomerate, and sandstone. They also derived from the Mount Dutton volcanic units. Con­ include all volcanic strata that exhibit primary dips resulting glomerate and sandstone occur as local channel fillings and from their emplacement by an active volcano onto the as lenses ranging from a few feet to a few tens of feet thick. flanks of its growing edifice. Vent facies rocks grade out­ Intertonguing with the vent facies, the alluvial facies has no ward into, and intertongue with, the alluvial facies, which complete section exposed in this quadrangle where its forms a broad apron of volcanic mudflow breccia and thickness is at least 1,000 feet (305 m). It thickens east­ subordinate conglomerate, sandstone, lava flows, and flow ward; along the west-facing scarp of the southern Sevier breccia. The map units, originally defined by Anderson and Plateau, about 5 miles (8 km) to the southeast, it is about Rowley ( 197 5), are described separately below. 3,000 feet (915 m) thick. Vent facies: