Abstract

The Zion National Monument in Washington and Iron counties, southwestern Utah, includes approximately 5000 feet of sedimentary rocks, profoundly and intricately eroded; extrusive volcanics of two ages; and faults and folds of large displacement. The oldest sedimentary formation exposed is the Kaibab (Permian). Above it lie the Moenkopi, the Shinarump, and the Chinle formations of Triassic age; the Navajo sandstone, assigned to the Jurassic; and the Carmel formation and Entrada sandstone of known Jurassic age. The igneous rocks are basaltic cones and lavas. In the western part of the Monument the pre-Tertiary Kanarra fold has affected all the sedimentary rocks exposed. The fold was broken essentially parallel to its axis by the Hurricane fault, which in late Tertiary and Quaternary times disturbed the sedimentary rocks and most of the lava flows. Generally east of the area traversed by the Kanarra fold and the Hurricane fault the rocks are nearly horizontal; the displacement produced by faults is relatively slight. The physiographic history of the region is substantially that of the Colorado Plateau, of which the Monument is a part. Two major cycles of erosion are outlined, each initiated by faulting accompanied by regional uplifts. Conspicuous erosion features are deep, vertically walled canyons, remnant flat lands, surfaces cut across tilted rocks, hog-backs, and thick accumulations of gravel on canyon floors, now in process of vigorous removal. The region has no permanent inhabitants; it is a reserved scenic area in the midst of summer grazing lands.

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