Lake Ivanpah: An overlooked pluvial lake in the southern Great Basin, U. S. A.

Abstract

A long-held but untested hydroclimatic model maintains that, in the arid southern Great Basin, U.S.A., hydrographically isolated watersheds held no late Quaternary paleolakes, even during pluvial periods. We test this model at Ivanpah Dry Lake, which has a watershed lying wholly within the mountains of the Mojave Desert, and no obvious ancient shorelines. Remote imagery was used to identify relict geomorphic features attributable to wave action during high-lake stands, and excavations in different parts of the basin margin revealed beach and lacustrine sedimentary sequences, some truncated by relict playa surfaces, most >2.5 m above the current playa. In the southern Ivanpah basin exposed lacustrine sediment grades upward to near-shore muds, capped by alluvium of the Cima Wash Delta-Fan. Time-dependent changes in carbon isotope ratios indicate that saltscrub (Atriplex polycarpa), the desert vegetation surrounding the dry lake today, did not become dominant until after 5.4 cal ka. A comparison of Paleolake Ivanpah’s initial radiocarbon chronology to regional hydroclimatic proxies demonstrates its potential to inform on changing sources of moisture contributing to pluvial events. This study shows not only that pluvial lakes occurred in the isolated watersheds of the Mojave Desert, but also that the margins of these basins are so geomorphically active as to entirely obscure the evidence of their occurrence. However, this process often buries and protects, rather than obliterates, geomorphic and stratigraphic evidence for past high-lake stands. It also shows that the basin margin, and not its depocenter, is where evidence of pluvial lakes should be sought. In the Ivanpah basin, some Holocene paleolakes appear to have persisted for decades to centuries.