Origin of ridge-top depressions by large-scale creep in the Olympic Mountains, Washington

In the high mountain area of the Olympic Mountains, Washington, there are many troughlike depressions on and essentially parallel to ridge tops. The troughs are mostly developed on rocks with strong planar anisotropy: slate, sandstone, and phyllite. Similar features in Europe, Japan, and New Zealand have been variously ascribed to erosion, slow movement along deep-seated shear planes, creep, and tectonic movements. In the Olympics, many depressions parallel structure; one wall is steeply dipping rocks, the other shattered, gently dipping rocks. These depressions seem to be the gaps left between undisturbed steeply dipping rocks and beds or cleavage bent valley-ward by creep. A few troughs may be the result of slow down-slope movement along deep-seated shear planes; this is a favorite explanation of eastern European workers. The Olympic ridge-top depressions testify to the importance of gravity in the degradation of high mountains carved from weak rocks.