PRELIMINARY MAP OF LANDSLIDE DEPOSITS IN THE MESA VERDE NATIONAL PARK AREA, COLORADO

Landslides are a dominant surficial feature in the Mesa Verde National Park area. More than 200 landslides, most previously unmapped and unrecognized, have been identified in the map area. These landslides range in size from small (0.01 km2) earthflows and rock slumps to large (greater than 1.25 km2) translational slides, debris avalanches, and complex landslides. Within the Mesa Verde National Park area many landslides occur in the Mancos Shale and Menefee Formation.

The Mancos Shale, a thick section (about 600 m) of mainly dark marine shale of late Cretaceous age, is prone to failure on steep slopes. Along the slopes of the northern and eastern escarpments the Mancos Shale commonly fails as debris flows and rotational or translational landslides. On these escarpments many of the slopes underlain by Mancos Shale are bare of vegetation, indicating very high rates of erosion and ongoing mass-wasting processes.

The Menefee Formation, about 200 m thick, consists of lenticular cross-bedded sandstone, carbonaceous shale, coal beds, and bentonitic clay beds, deposited in a broad coastal plain during the late Cretaceous. This formation forms steep colluvial slopes within the canyons of the park that are prone to failure and form many of the larger rotational or translational landslides within the park. One of these large landslides can be observed from Navajo Canyon Overlook. Here, the landslide pushed the ephemeral stream channel to the eastern side of the canyon, temporarily damming the canyon and forming a flat valley floor of alluvium on the upvalley side of the landslide.

Landsliding in the Mesa Verde area was probably more active during the Pleistocene, when the climate was wetter and cooler. However, landsliding is still an ongoing process in the park as evidenced by fresh scars in vegetated slopes along the northern escarpment. As the park has only one entrance road, which traverses a steep slope of Mancos Shale, a landslide along this slope has the potential to trap thousands of visitors inside the park. After an exceedingly wet Fall in 1978, a series of landslide movements along the east side of Point Lookout occurred during the spring of 1979 and closed the entrance road for more than a month.