The Precambrian basement of the Rocky Mountains foreland in Montana, Wyoming, Colorado, and New Mexico was closely involved in the Laramide deformation. During this deformation the basement was covered generally by 8,000-15,000 feet of sedimentary rocks. The dominant structural style of this region is basement block faulting of diverse trends and great structural relief. Individual blocks are bounded by upthrust faults which commonly die out upward into monoclinal flexures in the overlying sedimentary rocks.

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