Tectonic and Landscape Evolution of the Colorado Plateau

Chad Trexler

Abstract: The Colorado Plateau is a large, structurally intact, high elevation, tectonically enigmatic province that makes up a large part of the North American southwest. Approximately 90% of the Plateau is drained by the Colorado River and its tributaries, and evolution of the Plateau as a province is critical to understanding the formation of the Grand Canyon over the past 100 million years (Ma). Multiple, sometimes contradictory datasets have been used to argue for several versions of the history of the Colorado River Basin: that the Colorado River, more or less as we know it today, is responsible for carving the Grand Canyon over the last 6 Ma; that an ancestral, eastward-flowing ‘California River’ carved a portion of the canyon as long ago as ~70 Ma; or one of many variations and combinations of the two hypotheses. Though the debate is far from settled, most recent research suggests that some segments of the canyon conform to the ‘old canyon’ hypothesis, while others appear to be much younger; this has led to a new flurry of research attempting to provide a mechanism that could produce what is recorded in the geologic record. The dramatic geologic events recorded by the Colorado Plateau and the Grand Canyon provide context for the scale of human modifications to the Colorado River basin over the past half century.