Portuguese Bend Slide Zone (Rancho Palos Verdes, California)

USA / California / Rancho Palos Verdes / Rancho Palos Verdes, California
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Largest known translational slide in California. The flow zone covers some 260 acres. Early slide occured about 37,000 years ago, wherein the shear plane was parallel to the inclined bedding. Cause of the weakness unknown. Subsequent volcanic eruption produced an over burden of bentonite clay, which becomes plastic when wet. Some parts of the slide zone have moved over 200 yards since 1956.
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Coordinates:   33°44'21"N   118°22'1"W
This article was last modified 19 years ago