GEOLOGIC MAP OF THE TOOELE 30' X 60' QUADRANGLE—AN UPDATE TO THE GEOLOGIC HISTORY OF NORTHWEST UTAH

The Tooele 30' x 60' quadrangle, along the Interstate 80 corridor just west of Salt Lake City, was recently mapped by the Utah Geological Survey at intermediate-scale (1:62,500). The map area lies near the junction of several basement provinces likely associated with a large east-west-trending structural zone, which we call Uinta-Gold Hill, that was successively reactivated over time as indicated by the Tooele arch, Stansbury uplift, Uinta arch, and aligned Tertiary igneous rocks and mineralization. A thick sequence of Neoproterozoic and Paleozoic strata (12.5 km) accumulated on Paleoproterozoic basement rocks west of the hinge zone of the passive continental margin. We updated stratigraphic nomenclature for consistency across multiple thrust sheets of the Sevier fold-thrust belt. The map straddles two main Sevier belt segments—the Wyoming salient (north) and Provo or Charleston-Nebo salient (south)—and reveals new insights into the architecture and timing of thrust sheet emplacement. Subsequent calc-alkaline volcanism occurred from Paleogene volcanic centers (41 to 35 Ma) in the Stansbury and northern Oquirrh Mountains. Extensional tectonism created the distinctive basin and range topography from about 17 Ma to the present. There is evidence of basins containing Miocene sedimentary and volcanic rocks. Quaternary fault zones include the Puddle Valley, Stansbury, Oquirrh-Great Salt Lake, and West Valley; the Great Salt Lake fault zone was previously mapped using geophysical methods. Part of the map area was covered by extensive Pleistocene Lake Bonneville and now its smaller successor, Great Salt Lake. We mapped Lake Bonneville deposits and three levels of regional shorelines, but omit the lowest one (Gilbert) as a regional shoreline considering stratigraphic and geomorphic evidence. We also compiled key information on subsurface materials, and gravity, geochronologic, paleontologic, and geochemical data. This map is another important dataset to help decipher the complex geologic history of northwest Utah.