NEW GEOLOGIC MAP OF THE BROWNS HOLE 7.5' QUADRANGLE IN NORTHERN UTAH: DETAILED GEOLOGIC MAPPING IN AREAS OF HIGH POPULATION GROWTH AND UPDATING LEGACY MAPS

A primary goal of the Utah Geological Survey’s mapping program is to provide high-quality geologic maps of the Wasatch urban corridor at 1:24,000 scale. These maps require unique geologic mapping techniques and skills due to rapid urbanization, rugged terrain, access issues, and a long and complex geologic history. High-quality geologic maps provide foundations for geologic hazard, geotechnical, resource, environmental, and hydrologic studies, all of which support safe and sustainable growth. These maps also provide a fundamental geologic framework for a myriad of academic research. Originally published by Crittenden (1972) and later part of a 30' x 60' quadrangle (Coogan and King, 2016), the recently published geologic map of the Browns Hole 7.5' quadrangle (Anderson et al., 2023) is an example of a modern 1:24,000-scale geologic map in the Wasatch urban corridor.

The Browns Hole quadrangle is in the eastern part of Ogden Valley, Weber and Cache Counties, Utah. Here, exposures of the Willard thrust, a major thrust with approximately 50 km of eastward displacement that was active during the Cretaceous-Eocene Sevier orogeny, places Neoproterozoic through Ordovician strata in the hanging wall over Mesozoic strata. New structural data from the hanging wall of the Willard thrust suggest ESE shortening during the Sevier orogeny. New mapping provides an updated structural interpretation of relationships between major hanging wall structures and the Willard thrust. We provide an updated stratigraphic framework of Neoproterozoic and Lower Cambrian strata, which comprise a succession of clastic and carbonate rocks deposited during breakup of the supercontinent Rodinia and a rift-to-drift sequence of western North America. We reinterpret previous mapping of the Paleocene-Eocene Wasatch Formation, which unconformably overlies older rocks and was deposited over considerable paleotopography during late stages of the Sevier orogeny. We provide new, detailed mapping of lacustrine deposits and shorelines of Pleistocene-age Lake Bonneville. Newly identified Pleistocene glacial deposits, present in the northwest corner of the map, are likely related to the Pinedale glaciation. New mapping also identified multiple mass-movement deposits throughout the quadrangle, including historically active landslides.