Against the current— The Mojave River from sink to source: The 2018 Desert Symposium field trip road log

Abstract

The Mojave River evolved over the past few million years by “fill and spill” from upper basins near its source in the Transverse Ranges to lower basins. Each newly “spilled into” basin in the series? sustained a long-lived lake but gradually filled with Mojave River sediment, leading to spill to a yet lower elevation? basin. The Mojave River currently terminates at Silver Lake, near Baker, CA, but previously overflowed this terminus onward to Lake Manly in Death Valley during the last glacial cycle. The river’s origin and evolution are intricately interwoven with tectonic, climatic, and geomorphic processes through time, beginning with San Andreas fault interactions that created a mountain range across a former externally draining river. We will see and discuss the Mojave River’s predecessor streams and basins, its evolution as it lengthened to reach the central Mojave Desert, local and regional tectonic controls, groundwater flow, flood history, and support of isolated perennial stream reaches that host endemic species. In association with these subjects are supporting studies such as paleoclimate records, location and timing for groundwater and wetlands in the central Mojave Desert, and effects of modern water usage. The trip introduces new findings for the groundwater basin of Hinkley Valley, including an ongoing remediation project that provides a wealth of information on past and present river flow and associated development of the groundwater system.