An Unusual Glacial Event in the Comanch Peak Wilderness Area, Larimer County, Colorado

Abstract

Late Pinedale till deposits mapped in various stream valleys in the Comanche Peak Wilderness Area, north of Rocky Mountain National Park, indicate that Browns Creek Valley was glaciated from two directions simultaneously while the middle of the valley remained unglaciated. Till deposits at the upper end of Browns Creek Valley display a well-developed end moraine in a U-shaped valley. Immediately downstream from the end moraine the valley becomes V-shaped, and shows no evidence of glaciation. Another till is encountered in the lower reaches of Browns Creek Valley. This sediment was deposited by a distributary of the main valley glacier moving down Beaver Creek Valley. This subsidiary lobe of the Beaver Creek Valley glacier moved down gradient, but upstream. The tills are texturally distinct from alluvial deposits, but similar to each other. The tills are muddy and sandy boulder gravels, while the alluvial deposits that lie between them are sandy bouldery gravels. Although produced by two separate glaciers, glaciation of the upper and lower parts of Browns Creek Valley appears to have taken place simultaneously.

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