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Pressure Ridge, California

Pictures of Tectonic Landforms

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Pressure ridges form where lateral motions on a curving fault force rocks into a smaller space, pushing them upward. (more below)
A mole track from a large earthquake
Photo by Paul "Kip" Otis-Diehl, USMC, courtesy of the U.S. Geological Survey
Faults like the San Andreas fault are rarely perfectly straight, but rather curve back and forth to some degree. When a bulge on one side of the fault is carried against a bulge on the other side, the excess material is pushed upward. (And where the opposite occurs, the ground is depressed in a sag basin.) The Hector Mine earthquake of October 1999 created this small "mole track" pressure ridge in the Mojave Desert. Pressure ridges occur in all sizes: along the San Andreas fault, its major bends coincide with mountain ranges like the Santa Cruz, San Emigdio and San Bernardino Mountains.
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