_Mass-wasting_, the erosional process by which rock and soil move
downslope in response to the force of gravity, has also been
instrumental in shaping Palo Duro Canyon. This type of erosion has been
especially active on the walls of the canyon, for here the slopes are
steep enough to promote downward movement of earth materials. In a few
places there have been landslides which have moved large quantities of
rock in a short span of time. But most mass movements have been
imperceptibly slow as masses of _talus_ (accumulations of rock debris)
on steeper slopes have inched slowly downhill because of their own
weight. Talus deposits produced in this way can be seen at the foot of
most of the cliffs and erosional remnants throughout the canyon (fig.
20).