Comb Ridge, near Kayenta, Arizona

Comb Ridge, near Kayenta, Arizona, is a beautiful example of a monocline, a single-limbed fold. Monoclines are classic landscape features of the high deserts of the Colorado Plateau in the American Southwest. These folds were formed by dip-slip movement of rocks along deeply-buried faults about 65 million years ago, as tectonic forces compressed the crust and uplifted the Rocky Mountains farther east. They stand as evidence that continental regions that are seismically quiet now may have experienced deformation and earthquake activity in the geologic past. The view is to the east. Note the east-west fractures, visible near the center of the image, which formed when the relatively brittle rock was folded.

Contributed by Steven Semken, Arizona State University