Varied climatic and topographic influences on Late Pleistocene mountain glaciation in the western United States

The timing of Late Pleistocene mountain glacier fluctuations varied widely across the western United States. Glaciers in the maritime Olympic Mountains reached local maxima 125–60 ka and 34–31 ka, and were far less extensive during the global Last Glacial Maximum (LGM). Glaciers in the Cascade Mountains showed a similar general pattern but with contrasts in detailed timing. Most mountain glacier systems further inland exhibited maximum ice extent during Marine Isotope Stage (MIS) 2. In the Wallowa, Wind River, and possibly the Sawtooth Mountains, maximum ice extent occurred ca. 20–23 ka. Mountain glacier systems of the Cordilleran Ice Sheet (Puget Lobe), greater Yellowstone region and Uinta Mountains reached maximum extent ca. 19–16 ka, and those in the Wallowa, Sawtooth and Wind River Ranges were at near‐maximum positions ca. 17 ka. The variable timing of maximum and near‐maximum ice advances appears to be related to climatic setting and glacier mass balance characteristics. Mountain glacier systems under the strongest maritime influences reached maximum extent at times of strong westerly atmospheric flow. Olympic and Cascades glaciers appear to have been negatively influenced by weakened westerly flow at the time of the global LGM, perhaps associated with ice‐sheet‐induced anticyclonic flow. Glacier systems with maximum advances correlative with the global LGM appear to have responded more strongly to depressed temperature. The ca. 17 ka ice advances of several glacier systems are broadly correlative with Heinrich Event 1 in the North Atlantic region, and imply a cooling event and reinvigoration of moisture transport into the region. Post‐LGM advances of Uinta Mountain glaciers appear to have arisen from moisture influences of pluvial Lake Bonneville. Copyright © 2008 John Wiley & Sons, Ltd.