Late Quaternary geology and paleohydrology of pluvial Lake Mojave, southern California

A complex history of lake-level fluctuations is recorded in subsurface, cored lake deposits and shoreline features of Silver Lake and Soda Lake depositional basins of southeastern California. These basins are the location of former pluvial Lake Mojave and the present terminus of the Mojave River. The Silver Lake depositional basin is relatively shallow and has minimal relief across the pre-lake basin floor, resulting in a high resolution stratigraphic sequence that can be correlated in the subsurface and to the surface features. Radiocarbon-dated lake sediments from Silver Lake indicate that episodic flooding of the basin began as early as 22 ka with prolonged highstands lasting between 2000 and 3000 yr. Two major high and persistent lake stands occurred in the Silver Lake basin, and presumably in the Soda Lake basin, between ca. 18.4 ka and 16.6 ka (Lake Mojave I) and 13.7 ka and 11.4 ka (Lake Mojave II). These pluvial periods resulted from significantly increased precipitation and annual large-scale floods. The floods originated in the upper Mojave River drainage basin and reached Afton Canyon with discharge values two to three times larger than modern extremes. Periods of intermittent lake conditions during which the Silver Lake basin experienced several desiccation events separated the higher stands and more continuous Lake Mojave phases. The most significant drying event is recorded at 15.5 ka as large desiccation cracks infilled with windblown sand. During the earlier phases of its existence, Lake Mojave was the second of two large desert lakes sustained by the Mojave River; the other, Lake Manix, occurred upstream from Lake Mojave. Overflow from Lake Manix sustained Lake Mojave I which stabilized at the A-shoreline (elevation 287-288 m). The beginning of Lake Mojave II appears to have coincided with the incision of Afton Canyon and subsequent draining of Lake Manix, an event which significantly increased sediment loading, reducing totallake volume and increasing evaporative surface area. This condition resulted in significantly greater overflow of Lake Mojave into the Death Valley basin. This overflow produced controlled downcutting of the Lake Mojave outlet spillway between 12 and 11 ka and ultimately stabilized at an elevation of 285.5 m (B-shoreline). The majority of shoreline features currently found around the margins of Silver Lake and Soda Lake date to Lake Mojave II, as the shallow lake conditions resulted in modification and erosion of the older Lake Mojave I landforms. A transition to a drier climatic regime resulted in the total drying of Lake Mojave by ca. 8.7 ka, with playa conditions dominating Silver Lake and Soda Lake basins following this event. Analysis and correlation of the surface and subsurface environments of pluvial Lake Mojave yield a detailed reconstruction of the lake level elevation history as influenced by the discharge and floods of the Mojave River. Using a simplified, precipitation-discharge-evaporation model, we infer that the late Pleistocene hydrologic conditions resulting in Lake Mojave overflow at Spillway bay in Silver Lake lie between two sets of conditions: (1) a 50% increase in precipitation in the headwater catchment resulting in annual flood events reaching Afton Canyon with discharges three times that of modern extreme floods; or (2) a 100% increase in catchment precipitation with a 50% decrease from modern evaporation combined with annual flood events reaching Afton Canyon with discharges two times that of modern extreme floods.