Geologic Map of the Duchesne 30' x 60' Quadrangle, Duchesne and Wasatch Counties, Utah

This geologic map of the Duchesne 30' x 60' quadrangle is the result of five years of new mapping aided by previous mapping. Approximately centered on the town of Duchesne, Utah, the Duchesne County seat, the quadrangle covers most of the western Uinta Basin. Tertiary rocks of the Green River, Uinta, and Duchesne River Formations dominate the bedrock units in the quadrangle. Members of the formations are recognized and mapped throughout the Duchesne quadrangle despite the coarsening of these members in the western half. In the northwestern corner of the map area, Cambrian and Mississippian through Cretaceous rocks are exposed on the southwestern flank of the Uinta Mountains. The map area includes a variety of Quaternary-age surficial deposits including glacial deposits from the Uinta Mountains, multiple levels of stream and fan alluvium that record downcutting in the basin, and landslides. Major structural geologic features in the map area include (1) the Uinta Basin syncline and the related Uinta Basin fault zone, which locally offsets Quaternary deposits in the Towanta Flat graben, (2) the Duchesne fault zone, (3) nearly conjugant normal and oblique-slip faults in the northwestern part of the map area, and (4) north-trending normal faults along the western boundary of the map area. Unconformities in the Upper Cretaceous Mesaverde Group through the Eocene Duchesne River Formation record timing of the Laramide uplift of the Uinta Mountains and of the slightly older folding and faulting of the Sevier orogeny. The most significant geologic resources within the Duchesne 30' x 60' quadrangle are oil and gas from the prolific Altamont Bluebell and Monument Butte fields. Other exploited and potential geologic resources include phosphate, coal, sand and gravel, Gilsonite®, oil shale, and tar sand.