Problems of Stream Terrace Correlation and Reconstruction of Geomorphic History Caused by Colluvium

Abstract

The ability of colluvium to mask the presence of fluvial terrace gravel is examined in and near the Beartooth Mountains of southern Montana. Two areas, different in geologic setting, have been studied in detail to demonstrate the complications created by colluvium deposition when reconstructing the geomorphic history of each region. The colluvium is topographically indistinguishable from the stream deposits it covers. The presence of the buried terrace gravel is revealed only by careful field examination of subtle textural or compositional differences between the two types of material. Colluvial deposition occurred in both areas after fluvial aggradation ceased and before entrenchment by the main river commenced. The colluvium is not moving at the present time.