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Lake Temescal

Geologic Tour of Oakland, California

(c) 2004 Andrew Alden, licensed to About.com, Inc.

Oakland is full of vivid examples of fault behavior. Here is Lake Temescal, which began its historical existence as a sag pond—a place where two fault strands allow the rocks between them to sink. The early Anglo settlers dammed it to hold more water for the growing town, but for many years it has been left alone as the city secured better water elsewhere. The lake is now a park, including a fault exhibit and a short stretch of rare undisturbed creek bed.

The main strand of the Hayward fault runs along the near shore. We're looking west toward the bay; the far side of the fault is moving to the right. Consequently, Temescal Creek has been bent to the right. Just beyond the edge of the photo, the creek curves leftward and resumes its course (mostly underground these days). The ridge beyond the lake is called a shutter ridge, having blocked the mouth of the stream valley by fault movement.

See a view down the fault from this spot in the Hayward Fault gallery. The geologic map below shows the lake near the left edge. See where Temescal Creek enters the fault zone, at the bottom center of the map.

(c) 2004 Andrew Alden, licensed to About.com, Inc.

Download a 2400 by 2400 geologic map of Oakland (2 MB) for all the details.

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