Glaciers on the Colorado Plateau

An important indicator of climatic change on the highlands of the Colorado Plateau are glacial features such as moraines and glacial striations. These features, as well as others, are abundant in areas glaciated today, so their presence in some of the highlands of the Plateau indicates that in the past glaciers once flowed down a few of the region's mountains. Moraines form as glaciers grind their way downslope, forming a pile of rock debris at their base or along their side. Striations are distinctive linear streaks on bedrock that form as gravel and sand encased in the ice scours the underlying surface.

Glacier-scoured rock outcrops and Grass Lake on the Aquarius Plateau. Photo © 1998 Ray Wheeler.

A number of peaks and high plateaus on the Colorado Plateau were glaciated during the last major glacial period, the Wisconsin, which extends from approximately 65,000 years ago to about 15,000 years ago. The two highest areas on the Plateau, the San Francisco Peaks and the La Sal Mountains, have abundant moraines and cirque basins above 9500 feet, and are the only places on the Plateau that show classic alpine glacial topography. The San Francisco Peaks are one of the most southern mountainous areas to have been glaciated during the Wisconsin Period (the White Mountains and Sierra Blanca in New Mexico, both of which were glaciated, are a bit further south). The Boulder Top region of the Aquarius Plateau also exhibits evidence of past glaciation, with its scoured rock outcrops and numerous lakes.

Research:

Paleobotany and Paleoclimate of the Southern Colorado Plateau. The biota of the Colorado Plateau during the middle (50,000-27,500 B.P.) and late (27,500-14,000 B.P.) Wisconsin time periods was dramatically different from that seen today. Differences were primarily a result of major climate changes associated with the last major glacial period. This site examines the environment of the southern plateau during this time. Adapted by R. Scott Anderson from his journal article.