Glacial Geology of the Frying Pan River Drainage, Colorado

Abstract

On the west flank of the Sawatch Range, Colorado, evidence is found for six distinct glacial advances One glaciation is pre-Wisconsin, four are Wisconsin, and one post-Wisconsin in age. In addition to end and lateral moraines of each advance, terrace remnants of six valley trains were identified and studied for a distance of 25 miles along Frying Pan River and its major tributaries. Elevations above stream level of these outwash terraces are 400-450, 90-120, 50-40, 20-30, 12-17, and 6-8 feet. Five of the tributary valleys contained large ice streams which did not join the trunk Frying Pan glacier during the Wisconsin stage. Extensive review and testing of the numerous criteria used to distinguish deposits of multiple glaciations show that nine of these criteria can conveniently be expressed in parameters indicative of relative age. Estimates based on these criteria, coupled with a recent radiocarbon dating of late Mankato till in the Midwest, yield the following approximate ages for deposits of the six glaciations in Frying Pan Valley: 230,000, 63,000, 46,000, 17,000, 11,500, and 5,750 years. The accuracy and reliability of the procedure used cannot be evaluated without further absolute Carbon 14 age determinations.