LATE PLEISTOCENE GLACIAL HISTORY OF THE EAST RIVER, COLORADO WATERSHED

The glacial geologic record serves as one of the most robust indicators of terrestrial paleoclimate change. Furthermore, the extent, timing, and intensity of past glaciations can have long lasting impacts on critical zone and geomorphic processes. Mountain regions across the western United States, like the East River watershed near Crested Butte, Colorado, contain pristine records Late Pleistocene glacial activity and serve as evidence of the impacts repeated glaciations can have on landscapes. However, relatively few investigations of ancient glaciations have occurred in the East River watershed, and none have used modern cosmogenic exposure dating techniques. Here we present, 28 new in situ-produced ¹⁰Be exposure dates of glacial landforms, including moraines and striated bedrock, in the East River and Washington Gulch valleys. The ¹⁰Be ages will constrain the timing of local glaciation and ice retreat and allow for comparisons with nearby sites thus providing insight on the mechanisms controlling regional glacier change. We also use glacier modeling to reconstruct evolving ice-extents and climate conditions during the last glaciation. Further, the ¹⁰Be ages will temporally limit our glacier simulations and paleoclimate reconstructions which we will contrast with nearby climate proxy records and general circulation model results. Additionally, establishing the timing of deglaciation will constrain the timing of the onset of weathering in a catchment where critical zone processes and watershed function are being intensively investigated.