The Geology of the Skinner Peaks Quadrangle, Juab and Sanpete Counties, Utah

A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by Tracey Jan Felger in partial fulfillment of the requirements for the degree of Master of Science, March 1991. There are 3 supplementary files also attached to this record, which contain Plates 1 and 2 referenced in the thesis as well as a Correlation of Map Units.The geology of the Skinner Peaks 7 .5 minute quadrangle has been mapped at a scale of 1:24,000. The quadrangle is located m central Utah, just west of the leading edge of the Sevier fold-and-thrust belt, and in the transition zone between the Colorado Plateau and the Basin and Range. The stratigraphy and structure of the quadrangle reflect several tectonic events, including the Sevier Orogeny, monoclinal warping, and Basin and Range extension. Local diapiric movement of the Arapien Shale, which probably was initiated by these major tectonic events, further modified the structure and affected the stratigraphy. Exposed bedrock units in the quadrangle include sedimentary, pyroclastic, and intrusive rocks that range in age from Middle Jurassic to Late Oligocene. An unconformity separates Middle Jurassic marine strata of the Arapien Shale from the overlying Cretaceous-Tertiary strata. These Cretaceous-Tertiary strata include, in ascending stratigraphic order, the North Horn, Flagstaff, Colton, Green River, and Goldens Ranch Formations. Strata of the North Horn, Flagstaff, and Colton Formations represent the alluvial fan/plain, lacustrine, and alluvial plain/fluvial conditions that dominated the Sevier foreland basin from the Latest Cretaceous through Early Eocene. Eocene Green River strata record inundation of the basin by Lake Uinta, and the volcaniclastic Goldens Ranch Formation is representative of the widespread volcanism that was occurring throughout Utah during the Oligocene. Two small igneous intrusions also were mapped as were unconsolidated surficial lacustrine, fluvial, colluvial, alluvial fan, and landslide deposits ranging in age from Late Tertiary to Recent. Major structures m the quadrangle are West Gunnison monocline, the Juab Valley graben, the Sage Valley Fault, the Western Juab Valley Fault Zone, the Wasatch Fault Zone, and Flat Canyon graben. Economic deposits include sand and gravel, gypsum, tuff, carbonate rock, manganese, and water. Earthquakes, mass movements, karst development, and groundwater contamination are potential geologic hazards in the Skinner Peaks quadrangle