Counting marmots…
Cuesta scarp slopes on the Colorado Plateau developed in various lithological contexts and in different altitudinal belts were the subject of a long-term study. Specific attributes of the scarp slopes such as vegetation and soil cover, dissection density, activity of mass movements, talus production and general morphometry were documented. The principal aim was to investigate how these slope attributes change with increasing altitude and precipitation under the present climatic conditions and to use this information as an indicator of morphoclimatic changes during the Quaternary in a space-time substitution. Altitudinal shifts of the hydrological environment during the Wisconsin resulted in associated shifts of vegetation and morphoclimatic belts, and the lower elevations were affected by present high-altitude process combinations. Corresponding to their intrinsic lithological characteristics individual types of scarp slopes show different reactions to changing moisture availability. The specific response to changes in humidity is discussed using the example of a sandstone/mudstone (Dakota Sandstone/Brushy Basin Facies) scarp slope. This scarp slope was studied on the sides of a canyon (Cottonwood Canyon, Colorado), which follows the structural dip on the flank of a major uplift (Uncompahgre Uplift). Thus, as in an experimental setup, an elevation range from 1500 to 3000 m and an annual precipitation range from 200 to 600 mm are covered. In the semiarid altitudinal belt the moderately dissected slope has a convex profile with an average inclination of about 30°. With increasing humidity the convex slope profile disappears and mass movement activity and associated irregular slope forms become more and more obvious on the scarp slope, beginning with inactive or dormant landslides at elevations below 2500 m and precipitation amounts below 500 mm. In higher areas with rainfall amounts exceeding 500 mm, present-day mass movement activity can be observed. The lower limit of inactive landslides is indicative of how far humid phase mass movement processes extended down the sides of the canyon.
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