Late Quaternary glacial and paleoclimate history of the southern Uinta Mountains, Utah

It has been known for over a century that the Uinta Mountains contained numerous alpine glaciers during parts of the Quaternary Period, yet until recently, the glacial record on the south side of the range had received little scientific attention. Results of this 1:24,000-scale field mapping of surficial deposits in the southern Uinta Mountains indicate that glaciers in the southwestern and southeastern valleys were confined to deep canyons during the Last Glacial Maximum (LGM), whereas large glaciers in the south-central drainage basins extended beyond canyon mouths. Latero-frontal moraines marking the maximum advance of glaciers are best preserved beyond the mouths of the Lake Fork, Yellowstone and Uinta River Canyons. These landforms provide evidence of multiple Pleistocene advances. The youngest are the Smiths Fork and Blacks Fork Glaciations, which occurred during marine oxygen-isotope stages 2 and 6, respectively. An earlier (stage 16?) glacial episode, herein termed the Altonah Glaciation, is represented by an extensive lateral moraine beyond the mouth of Yellowstone Canyon.; A coupled 2-D mass balance and ice-flow numerical modeling approach to inferring paleoclimate from glacial records was applied to the Little Cottonwood Canyon in the Wasatch Mountains and the Lake Fork and Yellowstone Canyons in the south-central Uinta Mountains. Results of modeling experiments indicate that, assuming temperatures in the Wasatch and Uinta Mountains were ∼8--9°C colder than modern, corresponding precipitation changes were 0.7--1.5x modern in Little Cottonwood Canyon, 0.5--1.2x modern in Lake Fork Canyon, and 0.4--0.7x modern in Yellowstone Canyon. Greater amounts of precipitation in the Little Cottonwood Canyon likely reflect moisture derived from the surface of Lake Bonneville, but the mass balance of glaciers in the south-central Uinta Mountains was likely unaffected by the lake.; Cosmogenic 10Be-exposure ages of moraine boulders indicate the LGM in the south-central Uinta Mountains occurred at 17.6 +/- 1.1 cal. ka and, therefore, was approximately synchronous with the maximum extent of Lake Bonneville. This age also indicates that the Lake Fork and Yellowstone Canyon glaciers reached their maximum extents after the global LGM (21 +/- 2 cal. ka).