Wind River Basin
Almost exactly in the center of Wyoming is a rhomboidal topographic depression known as the Wind River Basin. Mountains and uplifts surround the basin, and nothing about the area is simple. The east and west sides of the rhomb are bounded by the northwest-trending Casper arch and Wind River Mountains, respectively; the north side is bounded by the Bridger-Owl Creek-Washakie ranges; and the south side is bounded by the Granite Mountains. In general, the basin is a highly asymmetrical syncline, with the basin axis nearest and parallel to the northern mountains and the Casper arch. The deepest part of the trough lies in the north, immediately adjacent to the Owl Creek Mountains, where the Precambrian basement may be displaced vertically more than 30,000 feet.
The western boundary of the basin is the east-dipping flank of the Wind River Range, characterized by northwest-trending hogbacks of Paleozoic sedimentary rocks. Structurally, the southern boundary is the northern flank of the Granite Mountains, defined by a series of northwest-trending features including the Rattlesnake Hills, Conant Creek, and Alkali Butte anticlines. These anticlines lie north of the North Granite Mountains fault system. Topographically, most of the southern boundary is a north-facing escarpment of Middle Eocene, Oligocene, and Miocene rocks known as Beaver Rim and Shirley Rim, an erosional feature analogous to the Pine Ridge escarpment in eastern Wyoming and Nebraska.
The Casper arch, a broad upfold of sedimentary rock, forms the eastern boundary. Topographic relief is low, but the rocks are greatly elevated relative to their depth in the Powder River and Wind River Basin on opposite sides of the arch. Exploratory drilling revealed that the west side of the arch is in the hanging wall of a thrust fault with low dip to the east. There is more than 5 miles of westward movement on this hanging wall, and the fault has actually overridden the synclinal axis of the Wind River Basin. Oil and gas production in deep reservoirs has been established in the footwall of this thrust fault.
The first oil well in Wyoming was drilled southeast of Lander at Dallas Dome in 1884, and oil has been produced from this and a series of northwest-trending anticlines along the western and northwestern edges of the basin ever since. Extensive oil and gas development has occurred in nearly all parts of this basin, and reservoirs of nearly every age have produced. The basin contains a thick sequence of Upper Cretaceous and lower Tertiary sedimentary rocks that contain important reserves of coal, oil, and especially natural gas.