The Uinta Mountains

Looking at a map of North America, one notices that the major mountain ranges trend north to south; this reflects the compressive, subduction and, in the case of fault-block ranges, stretching forces that produced the uplifts, which have generally come from an east-west direction. Two exceptions are the Transverse Range of Southern California, created by northward compression along the San Andreas Fault, and the Uinta Mountains of northeast Utah.

The Uintas, the highest range in the State, formed during the Laramide Orogeny (70-60 million years ago), which lifted the Rocky Mountain chain. Pressure within the North American craton, presumably secondary to the Farallon Plate subduction along the west coast, crumpled ancient Precambrian bedrock up through the overlying Paleozoic and Mesozoic sediments. Parallel faults in northeastern Utah, running west to east, dictated the unusual orientation of the Uinta uplift; furthermore, subsequent shifts in the crust forced the initial anticline northward atop the edge of the Green River basin, tilting the block. This latter movement, along a thrust fault, explains why the crest of the Uinta Range is much closer to its steep northern slope than to its more gradual southern slope. The uplift of this massive range also produced deep basins to its north, south and east, which held the Green River Lakes of the Eocene, among the largest freshwater lake systems in the history of our planet.

During the Pleistocene, glaciers scoured the summits of the range and produced broad, U-shaped valleys on its flanks, especially along the south side of the Uintas; this glaciation also created massive domes and flat expanses of tundra, with numerous glacial lakes, atop the range. Drainage along the south side of the Uintas is via streams that flow southeastward across the Uinta Basin to join the Green River, a major tributary of the Colorado; most streams on the north side also drain to this River though the western third of the north flank feeds the Bear River, which flows to the Great Salt Lake.