Line of Macomber Palms

October 26, 2005

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Provided and copyright by: David Lynch
Summary authors & editors: David Lynch

Extending for about 20 miles (32 km) through the desert in Riverside County, California is an irregular line oases with many Desert Fan Palm trees (Washingtonia filifera). These surprising moist areas mark the surface trace of the San Andreas Fault in the Indio Hills. Motion along the fault has shifted water-impermeable rock on the Pacific Plate against the alluvium of the Little San Bernardino Mountains on the North American Plate. Between the plates is a clay-like layer of fault gouge, rock pulverized by the grinding plates. Water flowing underground toward the Salton Sea reaches the fault zone and is blocked by the gouge. With no place to go, it backs up and rises to the surface, forming oases where the palms grow. Shown in the panorama above are the Macomber Palms, one of about two dozen groves and relatively lush areas of desert flora. The oases are elongated along the fault and represent one kind of so-called “vegetation lineaments,” common clues to the location of a major fault in a desert. Photo taken in March of 2004.

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