THE GEOMORPHIC ORIGIN OF THE GRAND VALLEY, COLORADO: A NEW APPROACH

The Grand Valley, which has an average valley width of ~7-8 km, has been a site of considerable geomorphic interest. Located in western Colorado, the Grand Valley is surrounded by the Uncompahgre Plateau, the Book Cliffs, and Grand Mesa. The origin of the Grand Valley has been the subject of much speculation and research attention past nearly forty years. With all the research that has been conducted, one would assume the question of origin of the valley had been answered — unfortunately no. Although the various studies have resulted in a large amount of data being compiled and various lines of arguments being undertaken to propose suggested origins, no definite proof of age or processes has been put forward. The exceptionally wide valley and its relative close location to the Grand Mesa, which was covered with an icecap during Pleistocene time, begs the question: Is there a relationship between glacial meltwater and the formation of the canyon?

Examination of the DEM of the area shows an overall flat terrain of the valley that extends some 7-8 km wide, which is in stark contrast to the width of the valley of the Colorado River in the same general area, which is less than 1 km in width. Previous research has suggested the erosion of the Grand Valley is the result of outwash cycles of Pinedale (MIS 2) and the Bull Lake (MIS 6) ages. Four terraces have been identified in the Grand Valley. Although similar terrace sequences in canyons in the area can be identified on imagery of the area, their correlation to the terrace sequence in the Grand Valley has not been undertaken. The proposed work will remap the terrace sequences in Grand Valley as well as in the other canyons in the area. In addition, radiometric dating of the various terraces will be undertaken to document the age and the relationship of the terraces to the periods of interglacial melt, as well as to each other.