Abstract

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 recent 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, whereas large glaciers in the south-central drainage basins extended beyond the mountain front. In contrast to the abundance of small valley glaciers on the north slope of the range, the south slope was dominated by six larger glaciers that attained areas in excess of 150 km² in the North Fork Duchesne, Rock Creek, Lake Fork, Yellowstone, Uinta River, and Whiterocks drainage basins. During the Last Glacial Maximum, these glaciers had maximum ice thicknesses of ~500 m. In addition, seven smaller valley glaciers (3.5 to 79.3 km²) occupied minor catchments in the southern Uinta Mountains.

Latero-frontal moraines marking the maximum advance of glaciers are best preserved below the mouths of Lake Fork, Yellowstone and Uinta canyons. These landforms provide evidence of multiple Pleistocene advances. The youngest are the Smiths Fork and Blacks Fork Glaciations, which, on the basis of cosmogenic dating and morphology of moraines, occurred during marine oxygen-isotope stages 2 and 6, respectively. An earlier (stage 16?) glacial episode, herein termed the Altonah Glaciation, is indicated by an extensive lateral moraine beyond the mouth of Yellowstone canyon as well as moraines in Lake Fork and Uinta River canyons. At higher elevations, alpine glacial landforms, including cirques, rock glaciers, aretes, and hanging valleys are ubiquitous.

Most glacial sediments on valley floors in the southern Uinta Mountains were deposited during the last deglaciation (~17.6 to 12 ka); these include moraines that may indicate a minor ice advance at ~13 ka in a south-central valley (Carson, 2003). In contrast, ice had disappeared from at least one valley in the eastern Uintas by ~14 ka (Munroe, 2002), indicating spatial variability in the responses of glaciers to latest Pleistocene climate change. Additional research aimed at identifying the time of the local Last Glacial Maximum and subsequent deglaciation in the southern Uinta Mountains is underway.