Abstract

The Laramie Basin is, in general, a northward-plunging syncline between the Laramie Range on the east and the Medicine Bow Range on the west. The dominant structural elements in the south end of the basin, near the junction of the ranges, are five northward-trending anticlines and the intervening synclines. The east flanks of three anticlines are cut by westward-dipping thrusts; northward, each thrust passes into a tear, which cuts westward across the axis of the anticline near the north end of the pre-Cambrian crystalline core. The thrust and tear constitute a scoop-shaped fault surface along which the block above the fault moved relatively upward to the northeast. The west flank of a fourth anticline is cut by an eastward-dipping thrust, which passes southward and eastward into a tear against which the pre-Cambrian core of the anticline terminates. It is believed that the folds, thrusts, and tears were formed under east-west compressive stress applied to a laterally uniform sheet of sediments overlying pre-Cambrian igneous and metamorphic rocks of varying competence.

Two en echelon synclines immediately east of the Medicine Bow Range are cut by westward-dipping thrusts. The west flank of the syncline has moved relatively east‐ward onto the east flank. Along the thrusts at the surface there are drag blocks younger than either of the two formations in contact along the fault.

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