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The Swallow Canyon 7.5-minute quadrangle is located on the north flank of the Uinta Mountains and the west part of Browns Park in northeast Utah and northwest Colorado (plates 1 and 2). The lower two-thirds of the quadrangle is occupied by mountainous terrain and the upper one third of the quadrangle is within Browns Park, through which the Green River flows. Swallow Canyon, the quadrangle’s namesake and named by John Wesley Powell during his historic 1869 expedition of the Green and Colorado Rivers, is a curious canyon that was cut by the Green River through a subtle bedrock spur that protrudes northward into Browns Park. The Swallow Canyon quadrangle contains a greater than 2-km thick (1.2mile) exposed succession of Neoproterozoic (Tonian) Uinta Mountain Group, strata of the Oligocene Bishop Conglomerate and Miocene Browns Park Formation, and an array of Quaternary surficial deposits. This map is largely a product of bedrock mapping from De Grey (2005), which includes facies, paleocurrent, and petrographic data, with paleogeographic and paleoenvironmental interpretations of the Uinta Mountain Group, and mapping of surficial deposits from Pederson and others (in preparation). |