TIMING OF LATE QUATERNARY GLACIATION AT THE EXTREME SOUTHERN MARGIN OF GLACIATION IN NORTH AMERICA, SAN GORGONIO MOUNTAIN, SOUTHERN CALIFORNIA

Moraines and associated landforms on San Gorgonio Mountain in the eastern San Bernardino Mountains of southern California mark the southernmost limit of glaciation in the Western Cordillera of North America. These landforms provide evidence for several glacial advances during the Late Quaternary. Cosmogenic radionuclide surface exposure dating of a succession of these moraines from three glaciated valleys define four glacial advances, which occurred at ~ 18 ka, 14-15 ka, ~12 ka and ~5-7 ka. These strongly correlate with Northern Hemisphere glaciation including glacial advances during the global Last Glacial Maximum, the Lateglacial, the Younger Dryas Stade and the early-middle Holocene. Our data suggests that glaciers develop and advance in this region when there is a significant decrease in summer temperature that is coupled with the considerable increase of in moisture supply and consequent high winter snowfall. This results in perennial snow accumulation that may persist to form glacial ice. This study highlights the importance of high moisture supply in sustaining glaciation in marginal regions. Furthermore, substantiates the view that glaciation throughout the American cordilleras was synchronous throughout the Late Quaternary.