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The Mount Powell quadrangle is located along the crest of the Uinta Mountains anticline in the High Uintas Wilderness Area. The quadrangle’s namesake, Mount Powell, is the seventh highest point in Utah at 4009 meters (13,153 feet). It was named for Major John Wesley Powell, a pioneering geologist who was the first to explore the Green and Colorado Rivers that later became the Geographical and Geological Survey of the Rocky Mountain Region during the late nineteenth century. The Mount Powell quadrangle was previously mapped by various workers. The quadrangle is dominated by unconsolidated surficial deposits of mostly glacial origin and the middle part of the Uinta Mountain Group (UMG), a succession of middle Neoproterozoic (ca 750 to 740 Ma) sedimentary rocks several kilometers thick. Bedrock units are exposed in the high peaks and steep cliffs and include (from stratigraphic lowest to highest) the Red Castle Formation, Dead Horse Pass Formation, Mount Agassiz Formation, and the informal formation of Hades Pass. The middle UMG strata exposed in the quadrangle indicate a paleogeography characterized by offshore, shoreface, nearshore marine, deltaic, and fluvial facies and stratal architecture. The sedimentary bedrock units are interpreted to have been deposited in fluvial and shallow marine environments within an epicontinental sea at least 150 million years before the latest Proterozoic inception of the Laurentian western passive margin.Glacial till of Smiths Fork age covers the basin floors, and related well-defined headwall cirques cut into bedrock at the heads of the basins. The flanks of the basins are somewhat covered by talus or rock glaciers and much of the high tablelands are covered by thin regolith that likely resulted from periglacial processes. The axis of the Laramide-age Uinta arch strikes through the quadrangle, gently folding the UMG bedrock units with generally shallow north and south dips (3 to 20 degrees). The Uinta crest fault parallels the axis of the Uinta arch through the quadrangle. Regionally, the Uinta crest fault is described as a down-to-the-north fault zone that extends from Hayden Peak, about 30 kilometers west-southwest of the Kings Peak 7.5-minute quadrangle to at least 30 kilometers northeast of the quadrangle. The UMG strata are also cut by minor (several meters of offset) to moderate (several tens of meters of offset) normal and reverse faults. |