INTERIM GEOLOGIC MAP OF THE RUSH VALLEY 30' X 60' QUADRANGLE, TOOELE, UTAH, AND SALT LAKE COUNTIES, UTAH

The Utah Geological Survey (UGS) is in the final year of STATEMAP-funded geologic mapping of the Rush Valley 30' x 60' quadrangle. This new geologic mapping supports coincident hydrogeologic studies of the Rush Valley area by the UGS and the U.S. Geological Survey. The quadrangle lies southwest of Salt Lake City in the eastern Basin and Range Province and covers several north-south trending, normal-fault-bounded, bedrock mountain ranges, including parts of the Oquirrh, East Tintic, Stansbury, Sheeprock, Simpson, and Cedar Mountains, and intervening parts of Cedar, Tooele, Rush, and Skull Valleys, and the Government Creek basin. This map combines new detailed geologic mapping with existing geologic mapping at 1:62,500 scale.

The bedrock geology of the quadrangle is characterized by a thick and laterally variable Neoproterozoic to Triassic sedimentary section. Sedimentary bedrock includes (1) Precambrian to Early Cambrian quartzite, shale, and conglomerate, (2) a thick sequence of Middle Cambrian to Mississippian limestone, dolomite, sandstone, shale, and quartzite, (3) Pennsylvanian to Early Permian interbedded limestone, sandstone, and quartzite, and (4) localized Triassic limestone, sandstone, and siltstone. These rocks were deformed into a series of broad north-south or northwest-southeast trending folds, and cut by generally east-directed thrust faults and east-west striking shear faults during the Late Jurassic to Eocene Sevier orogenic event. Sedimentary bedrock is locally overlain by Cretaceous to Eocene synorogenic deposits and is intruded and overlain by Eocene to Miocene generally felsic volcanic rocks. North-south striking Neogene normal faults cut bedrock and have controlled the formation of narrow, rapidly subsiding basins. Basin-fill in the map area includes (1) Eocene to Miocene? volcanic rocks, (2) consolidated to semiconsolidated Miocene tuffaceous lacustrine and alluvial deposits, and (3) unconsolidated latest Tertiary to Quaternary alluvial, colluvial, and lacustrine deposits. Late Quaternary lacustrine deposits document the transgression and regression of Lake Bonneville. Normal fault scarps cut pre- and post-Bonneville unconsolidated deposits parallel to mountain fronts in Rush and Skull Valleys.