The Las Vegas Formation was established a half century ago to designate the distinctive light-colored, fine-grained, fossil-bearing sedimentary deposits exposed in and around the Las Vegas Valley, Nevada. In a coeval designation, the sediments were subdivided into informal units with stratigraphic and chronologic frameworks that have persisted in the scientific literature. Use of the Las Vegas Formation name has been hampered because of the lack of a robust definition and characterization of the entire lithostratigraphic sequence, its geographic distribution, and chronology. In this study, we evaluated and described geologic deposits attributed to the Las Vegas Formation using detailed stratigraphy, sedimentology, and field relations. We also used accelerator mass spectrometry radiocarbon dating of charcoal and small terrestrial gastropod shells, as well as luminescence dating when required, to establish an unusually clear chronologic framework for the deposits.

In all, we characterized 17 informal geologic units within the formation, each dating to a unique period of geologic time, with stratigraphically ascending members X, A, B, D, and E and attendant beds in members B, D, and E. The age of the Las Vegas Formation spans at least the middle Pleistocene to early Holocene (from approximately 573 to 8.53 ka [thousands of years before present]) and is related to past groundwater discharge in the Las Vegas Valley. The contextual information derived from this new framework is dually noteworthy because the sediments entomb one of the most significant Pleistocene vertebrate faunas in the American Southwest, the Tule Springs local fauna, and represent a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Characterizing the nature of these important deposits stabilizes the nomenclature, promotes the continued use of these informal units, and facilitates studies of similar deposits associated with desert wetland ecosystems elsewhere in the southwestern United States.

Jeff grew up in central Illinois and didn't travel much as a child. In fact, he never even saw a mountain in person until he attended summer field camp in Red Lodge, Montana, at the age of 20. Needless to say, he was hooked immediately and has spent the last couple of decades making up for lost time. He received his B.S. degree from Southern Illinois University in Carbondale, and both his M.S. and Ph.D. degrees from the University of Arizona. He is currently the Project Chief of the Paleohydrology of Desert Wetlands project where he studies how desert wetland ecosystems responded to past episodes of abrupt climate change and is also the director of the brand new Radiocarbon Laboratory at the USGS right here in Denver.