GEOMETRY AND QUATERNARY HISTORY OF GIBBLER GULCH ARROYO, WESTERN COLORADO

Gibbler Gulch, an arroyo located on the northeast side of the Uncompahgre Plateau in Western Colorado, is characterized by a deeply-incised main fill terrace with a thickness of 20 meters. Stratigraphic sections through the arroyo fill reveal alternating sandy-clay and sand layers which are interpreted as the result of periodic aggradational flood events that eventually formed the main fill terrace. C14 dating of detrital charcoal in these layers indicates that aggradation began at least ~5,940 years ago and ended less than ~2,210 years ago.

Cut terraces in the lower part of the arroyo comprise basal horizons of gravel and a few sand layers that are much thicker than the thin layers of the main fill terrace. The cut terraces record incision, minor aggradation, and renewed incision. One C14 sample from a cut terrace fill indicates aggradation took place ~150 years before present.

The causes for incision and aggradation are not yet understood although similar C14 dates for aggradation and incision in the nearby Sieber Canyon arroyo support the hypothesis that regional climate change may have been an important factor.