Abstract

A pre-Cambrian area along Wind River Canyon has been exposed by faulting, uplift, and erosion. The country rock of the complex is schist, dipping about 40° S. It has been intruded by a mass of pegmatite and medium-grained granite, exposed at the north end of the area. Smaller apophyses of granite extend south from the main mass. Most of these are parallel or sub-parallel to the foliation of the schist. Apophyses farthest south parallel a joint system in the the schists, and are almost horizontal. Pegmatite predominates over medium-grained granite, and there is generally no systematic relation between the two. Foliation in the granite is uncommon. Jointing in the main body of granite suggests a stock-like form.

The intrusion was accomplished without pronounced change of the surrounding rock. Injections of the lit-par-lit type are uncommon. The metamorphic country rock has been forced apart and crowded to the south by the granite. It is suggested that the east-west fault or fault zone paralleling the southern margin of the mountains might have had its inception in this southward crowding of the intruded rock. Whatever the subsequent history, the faulting would thus have had its start in the pre-Cambrian.

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