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Geologic Map
Shaded Relief
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Generalized Geologic Map of the Conterminous United States
North America Shaded Relief


  The North American Tapestry of Time and Terrain

The Two Maps
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Legend and Rock Ages
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Garlock Fault


Close-up of
 the Garlock Fault region










The intersection of the San Andreas (the blue line) and Garlock (orange line) faults in southern California reflects two different tectonic forces: the northwest-southeast sliding along the boundaries of the Pacific and North American plates, and the roughly east-west crustal extension within the North American plate. The relative westward movement of crust north of the Garlock fault bends the San Andreas system into a lazy "S" pattern. This deflection results in a compression of rocks to the south of the fault, pushing them upward, as expressed by the San Gabriel Mountains and the east-west trending Transverse Ranges north of Los Angeles.