Structural Relationships of Northern and Central Parts of Emigrant Gap Anticline, Natrona County, Wyoming: ABSTRACT

Emigrant atGrap anticline lies on the east side of the Casper arch and trends north-northwest in east-central Natrona County, Wyoming, from the western end of Casper Mountain to its plunge south of Petrie Siding, a distance of about 20 mi. Outcrops of Cretaceous Frontier sandstones define or outline the structure, especially its northern and central parts. Surface expression of faulting is minor; some beds are repeated by minor thrusting, and some are offset by small mainly north-northeast strike-slip faults. Joint sets include an approximately horizontal set, a high-angle northeastern set, and a high-angle northwestern set. A fourth high-angle approximately east-west set is prominent only in one area where the anticlinal axis is sinistrally offset almost 2 mi. An unexposed strike-slip/wrench fault is probably present at depth and probably offsets one or more major subsurface thrusts. These include the Owl Creek thrust fault, which extends beneath Pine Mountain, and probably one other east-dipping thrust that has possible surface extension adjacent to the anticline. Emigrant Gap anticline appears to be rootless, having been transported westward as part of a thrust sheet during the Laramide orogeny, the principal compressive stress directed east-northeast to west-southwest. Blind strike-slip or wrench faults probably offset the thrustmore » sheet.« less