THE GEOLOGY, PALEOHYDROLOGY AND FOSSILS OF TULE SPRINGS FOSSIL BEDS NATIONAL MONUMENT, NEVADA: A LATE PLEISTOCENE TREASURE TROVE

Tule Springs Fossil Beds National Monument (TUSK), designated in December 2014, preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley. The Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene vertebrate assemblages in the American Southwest, is entombed in stratigraphically complex groundwater discharge deposits, which provide evidence of past desert wetland ecosystems throughout the new monument. In 2008, the San Bernardino County Museum initiated a large-scale paleontological and geological study that resulted in the discovery of hundreds of fossil localities and recovery of thousands of fossil specimens, greatly extending the spatial and temporal footprint of investigations from the 1960’s. Mammuthus, Camelops, Equus, and Bison dominate the fauna. Megafaunal carnivorans include Panthera, Smilodon fatalis, and Canis dirus. Smaller organisms include amphibians, snakes, birds, and micromammals.

Investigations focused on detailed stratigraphic analysis, geologic mapping and targeted dating with the goal of establishing the context for the fauna and integrating the TSLF into a rigorous lithostratigraphic and geochronologic framework. In collaboration with the USGS, we established a highly resolved chronology based on ¹⁴C dating of charcoal and luminescence dating of sediments. We also redefined and established new geologic units within the informally named Las Vegas Formation. Our results show that ground-water discharge deposits in the region record dramatic hydrologic changes in response to abrupt climate oscillations during the late Pleistocene, including the repeated growth and collapse of entire wetland systems. The hydrologic response of the Las Vegas paleowetlands demonstrates a tight correlation with Greenland/North Atlantic climate proxy data on a sub-millennial scale. This is the first record to demonstrate millennial and sub-millennial scale climate oscillations in groundwater discharge deposits, which are fairly common through the southwestern U.S.

The newly established Tule Springs Fossil Beds National Monument therefore preserves these linchpin deposits and their attendant fauna in the upper Las Vegas Wash for posterity, and our scientific results provide a powerful interpretive springboard for the new monument.