GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION DISTINGUISHED CAREER AWARD 2020: 40 YEARS SEARCHING FOR ROUNDED GRAVELS: DRAINAGE CHANGES, FLOODS, AND BIG LAKES

The hydrologic features of landscapes in the western United States are in a constant state of adjustment to external forces of tectonics and climate change. These adjustments are commonly recorded by gravels and finer-grained deposits and include: (1) varying lake highstands, caused by pluvial periods of different intensities, that often resulted in (2) drainage integration by filling and spilling of successively lower basins with water and sediment, sometimes catastrophically, and (3) rearrangement of drainages by stream capture. Beach gravels and associated finer sediments reveal that many basins—but not all—in the western Great Basin held much larger lakes at times prior to the last pluvial highstand period (~15-18 ka, Marine Isotope Stage [MIS] 2), and these high lakes sometimes caused overflow. Ages of the pre-MIS 2 lakes have been constrained in some locations by paleomagnetic, tephrochronologic, radiometric, and cosmogenic exposure dating. What climate conditions drove these highstands and why did some lakes apparently not respond? Most of the lake basins in western and central Nevada, eastern California, and one basin in southeastern Oregon show evidence of at least one older higher lake that stood a few meters higher than the MIS 2 lake and in a few places has been dated to MIS 4 and (or) 6. Some lake basins, including Lahontan, Columbus-Fish Lake, Mono, Newark, and Long, record evidence for even larger pre-MIS 6 lakes. The exceptions thus far are mainly the northeasternmost basins in Nevada (Waring, Clover, Independence, and Spring valleys), which suggests that geographic location may play a role, perhaps related to atmospheric circulation and moisture source. More field work is needed in some basins of central Nevada and in several Oregon basins, as well as better age control, to test this hypothesis.