The Rocky Mountain area of the western United States presents the most complete record on this continent of geologic events from Archean time to the present. Sediments from all the major periods are known somewhere in the region and the excellent outcrops have made possible their detailed examination. Many geologists have worked there and the literature is vast.

This paper is an attempt to summarize it all and to present a continuous story of geologic conditions and happenings in the Rocky Mountains from the pre-Cambrian to the Recent. This will be done with a series of paleogeographic maps and cross sections, and the stratigraphy will be described more fully than the structure. Four major events controlled the geology of the Rocky Mountain area.

  1. The formation, in Algonkian time, of the Cordilleran geosyncline which extended from Utah to British Columbia and persisted in that position through all geologic periods to the end of the Upper Cretaceous.

  2. The extension in the Pennsylvanian and Permian of the Arbuckle-Wichita-Amarillo line of mountains into New Mexico, Colorado, Utah, and Wyoming and their subsequent erosion and burial under Triassic and Jurassic sediments.

  3. The uplift, in the Middle Triassic, of the Cordilleran land mass on the west and southwest which furnished sediments from those directions throughout the remainder of Triassic and all of Jurassic and Cretaceous time.

  4. The extension eastward, at the close of the Upper Cretaceous, of the uplifted, folded, and faulted Cordilleran highland until the present Rocky Mountains were formed in the geosynclinal area and the sea was finally pushed from the interior of North America.

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