THE PATTERN OF PLEISTOCENE MOUNTAIN GLACIATION IN THE INTERIOR GREAT BASIN, WESTERN UNITED STATES

The record of Pleistocene glaciation in the Great Basin spans more than forty mountains and represents a useful proxy for paleoclimate. Historically, the glacial record in mountains of the interior Great Basin of western Utah and Nevada have received less attention compared to the glacial record along the margins of the region in eastern Utah and California. Here, we report the spatio-temporal pattern of mountain glaciation in the Great Basin interior based on mapping of glacial deposits and landforms, cosmogenic ¹⁰Be exposure dating of glacial deposits and landforms, and numerical modeling of known ice extents in multiple mountains. In northwestern Nevada, small valley glaciers in the Santa Rosa and Pine Forest Ranges occupied terminal moraines until 21-18 ka, and readvanced to or persisted at near-maximum lengths until 17-15 ka. In eastern Nevada, a similar temporal pattern is observed in the Ruby and East Humboldt Ranges, where terminal moraines were occupied until 22-19 ka and downvalley recessional moraines representing readvances were occupied until 18-16 ka. In the South Snake and Deep Creek Ranges near the Nevada-Utah border, terminal moraines were occupied until 20-19 ka. Numerical modeling of glacial mass balance and ice flow in the Ruby, East Humboldt, and South Snake Ranges suggests that the earlier glacial episode was accompanied by temperatures 9-11°C less than modern and near-modern precipitation. During the latter glacial episode, which corresponded in time to pluvial lake highstands in eastern Nevada, temperatures were likely 1-3°C warmer than during the earlier episode with precipitation rates at least 30-50% greater than modern. After downvalley moraines were abandoned at 16 ka, glaciers retreated to cirques by 14-12 ka and, in one valley in the East Humboldt Range, persisted until as late as 10 ka. Consistency in the pattern of mountain glaciation throughout the interior Great Basin suggests regional-scale drivers of climate change during the last glaciation and early deglaciation.