Abstract

Morphologic evidence in an unusual boulder field in the Flint Creek valley of western Montana, previously classified as glacial moraine, suggests a debris flow deposit carried from Boulder Creek, a tributary of Flint Creek. A large flood from a cloudburst in the headwaters of Boulder Creek or a moraine-dammed lake in a cirque in the upper stream system surged down the main Boulder Creek valley, picking up glacial debris and depositing it in lobate form in the Flint Creek valley. Other boulder deposits in western Montana and elsewhere with similar morphologic characteristics may also be of fluvial, rather than glacial, origin.

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