Abstract

The Traverse Mountain and Hogup Mountain field sites, located in northwestern Utah, provide well-preserved shoreline records from Pleistocene Lake Bonneville during the last glacial maximum. These shoreline deposits and associated landforms (e.g., baymouth barriers, beach ridges, spits, tombolos, and wave-formed benches) retain their geomorphic expression along with internal lithologies and sedimentary structures. Field mapping, stratigraphic analysis, and aerial photograph interpretation were utilized to reconstruct depositional and geomorphic histories at Traverse Mountain. This study distinguishes nine lithofacies, including three foreshore/shoreface gravel facies, five shoreface sand facies, and an offshore silty marl facies. All nine facies are present in Traverse Mountain field area and were deposited during the transgressive phase of the Bonneville lake cycle (24-14.5 ka ¹⁴C yr B.P.). Storm-dominated circulation energies, sediment supply, slope/basin physiography, shoreline shape, and lake level controlled development of the lithofacies at Traverse Mountain. Distinctive landforms developed during the Bonneville lake cycle are preserved at Traverse Mountain. The five major controls on beach ridges and wave-cut platform development in the two field areas include slope/basin physiography, sediment supply, shoreline shape, climate, and isostatic deflection. At Traverse Mountain, steep basin physiography helped create more accommodation space, so sediment was deposited close to the shoreline as spit platforms. In areas with shallow basin physiography and hence little accommodation space, such as Hogup Mountain, sediment was easily deflected and distributed over a laterally extensive area to develop more substantial beach ridges. These well-exposed Pleistocene examples illustrate the important interplay between various controls on sedimentation in a large lake system.