Grand Canyon Bight--Significant Tectonic Feature of the Southwest: ABSTRACT

Abstract

A bight, by definition, is a curve in a coastline, or a bend, angle, or corner in any configuration. This seems to be descriptive of the dominant tectonic feature of southwestern Utah, northwestern Arizona, and a small adjacent tract of Nevada. The Grand Canyon is the best-known local geographic feature of the region, hence the name Grand Canyon bight. The Grand Canyon bight is the somewhat drawn out and distorted southwest corner of the Colorado Plateau; more importantly, it is a region of relatively simple structure between the converging Wasatch line on the north and the Central Arizona uplift (Mogollon rim?) on the south. These great structural trends approach each other but, due chiefly to the change of direction of the Wasatch line from southerly to westerly and the dying out of the Central Arizona uplift, they do not merge and there is a space of relatively simple structure between them. The bounding tectonic features came into topographic prominence when the Mesocordilleran highland was elevated in Middle Triassic time. Subsequent sedimentary deposits, especially the marine and fluvial formations, are strongly influenced by the bight. Cretaceous shorelines and isopachs show this influence particularly well. The river system which deposited the Salt Wash Sandstone Member of the Morrison Formation entered the region of the Colorado Plateau through the Grand Canyon bight; the present Colorado River leaves the bight in a reverse direction. Other geologic references also are simplified by recognition of the Grand Canyon bight as a tectonic entity. End_of_Article - Last_Page 656------------