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Stream Piracy in Peachtree Valley

Creeping Segment of the San Andreas Fault


Stream piracy created this canyon at the head of Peachtree Valley west of the San Andreas fault. View west. (more below)
A worthy sideshow
Photo (c) 2007 Andrew Alden, licensed to About.com (fair use policy)
At the Peachtree Valley's southern end, we can turn our attention from the San Andreas fault and enjoy a spectacular example of stream piracy. The flat floor of the valley, visible at right, gives way to a deep canyon carved by Poncho Rico Creek as it eroded its way headward through the low ridge bounding the valley on the west. Quickly it diverted the headwaters of San Lorenzo Creek, and the extra water power cut the river bed far below its previous level. Stream capture is a common way for fish species to move into new territory—or to be isolated from other populations.

In the foreground is the hummocky ground of a large landslide scar. Whatever quantity of material slid into the canyon, Poncho Rico Creek evidently had no problem carrying it away.

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