INTERIM GEOLOGIC MAP OF DUGWAY PROVING GROUND AND ADJACENT AREAS, TOOELE COUNTY, UTAH

The Utah Geological Survey (UGS) completed an intermediate-scale (1:75,000) interim geologic map of Dugway Proving Ground (DPG) and adjacent areas. This is the first complete geologic map of DPG, a U.S. Army installation involved in chemical and biological testing and training. The map area also includes parts of the Utah Test and Training Range used for U.S. Air Force operations, and the Cedar Mountains Wilderness. This project is part of ongoing work by the UGS to complete mapping of the 30' x 60' quadrangles in Utah, and includes parts of the Wildcat Mountain, Rush Valley, and Fish Springs quadrangles. We mapped the extensive Quaternary surficial deposits related primarily to Lake Bonneville, eolian, alluvial, and mixed depositional environments, and three of the four major shorelines of Lake Bonneville (Stansbury, Bonneville, Provo); there is no geomorphic expression of the Gilbert shoreline. Eolian sand forms extensive sheet and dune complexes adjacent to several mountains. The vast mudflats of the Great Salt Lake Desert were mapped as a stacked unit of eolian and alluvial deposits over lacustrine fine-grained deposits (Qea/Qlf). The mudflats contain channel systems related to the Old River Bed delta, which formed between about 11,000 and 9,000 ¹⁴C yr B.P. where a paleoriver entered the Great Salt Lake basin following the final regression of Lake Bonneville. Bedrock units range from Miocene to possibly Neoproterozoic in age. New ⁴⁰Ar/³⁹Ar ages on Tertiary volcanic rocks show the rhyolite of Sapphire Mountain and rhyolitic dikes in Granite Peak are 8 Ma, while the southern Cedar Mountains volcanic center (composed of andesitic and dacitic intrusive, extrusive, and sedimentary rocks) is from 38 to 41 Ma. Granite Peak (aka Granite Mountain) was shown to be Late Jurassic (149 Ma) in age through U-Pb zircon dating done for prior UGS mapping. The numerous Paleozoic sedimentary rock units range from Permian to Cambrian age; distinct packages are distributed between at least three main thrust sheets. The Permian-Pennsylvanian Oquirrh Group in the southern Cedar Mountains was remapped using lithologic and fusulinid fossil control to conform to the nomenclature developed in the Bingham Mine area. Metamorphic rocks at the south end of Granite Peak are likely from Paleozoic or Neoproterozoic protoliths.