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Stream Offset, California

Pictures of Tectonic Landforms

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Stream offsets are the counterpart to shutter ridges, a sign of lateral movement on strike-slip faults like the San Andreas fault. (more below)
Crooked creeks
Photo courtesy Alisha Vargas of Flickr under Creative Commons license
This stream offset is on the San Andreas fault in Carrizo Plain National Monument. The stream is named Wallace Creek after geologist Robert Wallace, who documented many of the remarkable fault-related features here. The great 1857 earthquake is estimated to have moved the ground sideways about 10 meters here. So earlier earthquakes clearly helped produce this offset. The left bank of the stream, with the dirt road on it, can be considered a shutter ridge. Compare this picture to the shutter ridge picture, which is exactly analogous. Stream offsets are rarely this dramatic, but a line of them is still easy to detect on aerial photos of the San Andreas fault system.
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