TESTING AND REFINING THE TIMING OF HYDROLOGIC EVOLUTION DURING THE LATEST PLEISTOCENE REGRESSIVE PHASE OF LAKE BONNEVILLE

Lacustrine, fluvial, and wetland landforms present in the now desertified regions of Dugway Proving Ground (DPG) and the Sevier Desert (SD) in western Utah, record a fascinating history of falling lake level, river development, and establishment of wetland habitats in the Lake Bonneville basin between ~14-8 ka ago. This was not only a time of rapid climate change but also of human occupation into suitable habitats made available by decline of the large lake. Using optically stimulated luminescence (OSL) dating methods we are determining depositional ages for sediment samples from bar features (reworked deltaic sands), braided fluvial channels, and topographically inverted fluvial channels collected from DPG during prior fieldwork. These data will be compared to existing chronological evidence from DPG and SD to test and refine the timing of changes in the geologic environment during this stage of Lake Bonneville regression. Accurate assessment of the timing of the hydrological and geomorphological changes taking place during the late regressive phase of Lake Bonneville will help determine the relative importance of environmental change compared with groundwater discharge thought to accompany falling lake levels.