NEW GEOLOGIC MAP OF THE KAMAS 7.5′ QUADRANGLE, WASATCH BACK, UTAH: INSIGHTS INTO TECTONIC EVOLUTION, PALEOGENE VOLCANISM, AND QUATERNARY DEPOSITS

The Kamas 7.5′ quadrangle, located in the Wasatch Back about 30 miles east of Salt Lake City, Utah, is characterized by a complex geologic setting shaped by tectonic, volcanic, and depositional processes. Centered around the north-south-trending Kamas Valley, the quadrangle includes the cities of Kamas and Oakley, as well as the town of Peoa, and is nestled between the Uinta Mountains to the east and the West Hills of the Keetley volcanic field to the west. The Kamas Valley and Wasatch Back are experiencing increasing development pressures, and this map provides detailed geologic information essential for land-use planning, hazard assessment, and resource management.

The Kamas quadrangle lies at the western terminus of the east-west-oriented Uinta arch. The Uinta arch, a Late Cretaceous to Paleogene Laramide basement-cored uplift, influences the region's structural framework by folding and steepening pre-existing Paleozoic and Mesozoic stratigraphy and interacting with thin-skinned Sevier structures. Subsequent Paleogene volcanism blanketed much of the region with intermediate to felsic Keetley volcanic rocks. The Keetley volcanic field is dominated by lahar and debris avalanche deposits, lava flows, and ash-fall tuffs. Keetley volcaniclastic deposits are particularly prone to landslides and mass movement. In the southwestern corner of the map area, the Indian Hollow stock and the associated radial dike swarm mark the eastern terminus of the Wasatch intrusive belt and are considered the source of the Keetley volcanic deposits.

The East Kamas Valley fault, a concealed normal fault along the valley's eastern margin, reflects Neogene Basin and Range extension and creates and bounds Kamas Valley. Kamas Valley is a structural half graben filled with extensive glacial outwash and alluvial deposits, including large alluvial fans sourced from the Uinta Mountains. Pleistocene glacial episodes deposited two distinct outwash units in the valley. Although no major river flows north-south through the valley today, geomorphic features of the younger glacial outwash deposits suggest a paleo-south fork of the Weber River, now the upper Provo River, once flowed north through the valley.