Great Basin Naturalist


Owens Valley, California, was markedly different during the Wisconsin glacial stage from what it is today. Alpine glaciers bounded the Sierra Nevada, and pluvial Owens Lake reached highstands and overflowed its natural basin. We analyzed three layers from two packrat middens, dated to ca 23,000–14,500 yr BP, obtained from Haystack Mountain (1155 m) only 10 m above and <100 m from the highstand strandline of pluvial Owens Lake. During this period vegetation near Owens Lake reflects the influence of the Tioga glacial advance and retreat on lake levels, and microclimatic effects on shoreline vegetation. Between ca 23,000 and 17,500 yr BP a Utah juniper (Juniperus osteosperma) and single-needle pinyon pine (Pinus monophylla) woodland existed at the site. In the layers dated to ca 17,500 and 16,000 yr BP, macrofossils document the presence of Rocky Mountain juniper (Juniperus scopulorum), a species that no longer occurs in California. It is suggested that meltwater from the retreating glacial ice inundated the Owens River Lake chain causing pluvial Owens Lake to reach its highstand. This caused an increase in effective moisture, due to high groundwater, allowing the mesophytic Rocky Mountain juniper to exist at the site.