Abstract

The Wind River Range, Wyoming, the largest discrete element of the Wyoming foreland, is a doubly plunging anticline bounded on the southwest by a low angle thrust fault. The range is approximately 140 miles long and 35 miles wide. The thrust fault reflects two principal foreland trends, one N.40° W. and the other N.70°W. Tectonic transport is 16 miles laterally; vertical separation is 9.3 miles. The range core consists of Precambrian greenstones, migmatites, gneisses and granitic plutons ranging in age from 3.4 to 2.3 billion years. Persistent shear zones trend N.20°W. at an angle of 20° to the range orientation.

Deformation began in Late Cretaceous (Lancian), climaxed in Eocene (Wasatchian) and terminated in Eocene (Bridgerian), prior to extensive ash falls in Oligocene. Extensional tectonism (post-Miocene) resulted in the Continental Fault system, restricted to the hanging wall of the major thrust fault. Normal faults are down to the north (mountainward); listric, concave up in form; offsets range up to 1500 feet.

At least two "high level" erosion surfaces exist. The higher, Fremont, is the exhumed Precambrian-Cambrian interface. An extensive, severely glaciated surface flanks the range on the west and carries up to the Continental Divide. This surface is reported to be as old as Eocene, or as young as Mio-Pliocene. The latter age best fits the pattern of maximum basin fill prior to superposition of major drainage in Wyoming. The existence of an Oligocene compressional tectonic event that elevated the core of the range is questionable.