A GEOMORPHOLOGICAL-SEDIMENTOLOGICAL INTERPRETATION OF ARMORED DEPOSITS ALONG THE SOUTHERN FLANKS OF GRAND MESA, CO, USA: A PRELIMINARY ASSESSMENT

A series of deposits located along the southern flanks of Grand Mesa, Colorado, and extending to the south are a series of pediment surfaces that are problematic. The overall area is dominated by two landform systems, Grand Mesa, which supported a Pleistocene ice cap, and the North Fork Gunnison River drainage. Thus, one has to ask: Are these deposits enhanced by the melting of the ice cap or are they fluvial terraces associated with the evolution of the ancestral Gunnison River? We hypothesize that the deposits were modified during late Pleistocene climatic warming. Our objective was to map the areal extent of the deposits and to interpret their formation and climatic significance in understanding the evolution of Pleistocene/Holocene landscape in the region.

An excellent exposure parallels CO 65 near Cory Grade and was used for detailed description and sampling.  Additional exposures near Hotchkiss, Colorado, were used to extend our sampling. The study area was mapped using aerial photography and traditional field mapping aided with GPS. These data along with geology, soils, land cover, topography and slope maps were entered as data layers into a Geographic Information System (GIS) and used to create derivate maps for subsequent analysis. A detailed stratigraphic column including lithology, grainsize analysis, and erodability was constructed based on fieldwork during Summer 2009. Vertical exposures of the deposits were mapped in detail. Samples were gathered from each stratum of the deposits for grainsize, shape, and sorting analyses. Distinct layers showing different depositional regimes were identified. We were unable, unfortunately, to locate datable materials during this stage of the investigation.

Sorting and faint imbrication suggest a probable source area to the north, i.e., Grand Mesa. We think this study will add an important piece in the understanding of the landscape evolution of the region. In the future, we will use the Immersive Visualization Center (IVC) to create a dynamic three-dimensional model of the deposition.