Geologic Setting


Merced Formation (lower Pleistocene and upper Pilocene



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Merced Formation (lower Pleistocene and upper Pilocene) is a medium-gray to yellowish gray and yellowish orange, medium to very fine-grained, poorly indurated to friable sandstone, siltstone, and claystone, with some conglomerate lenses and a few friable beds of white volcanic ash. In many places, sandstone is silty, claylike, or conglomeratic. Some of the conglomerate, especially where fossiliferous, is well cemented. Volcanic ash is in beds as much as 2 m thick and consists largely of glass shards (USGS).


Serpentine is a greenish-gray to bluish-green sheared serpentine, enclosing variably abundant blocks of unsheared rock. Blocks are commonly less than 3 m in diameter, but range in size from several centimeters to several meters; they consist of greenish-black serpentine, schist, rodingite, ultramafic rock, and silica-carbonate rock, nearly all of which are too small to be shown on the a map (USGS).
Due to erosion, slumping, and faulting in the area, the poorly cemented Merced sediments have been reduced into a large active landslide. Landslide deposits in this area create many small knolls in the topography that are heavily vegetated. Steep cliffs, most of which are either landslide or fault scarps, surround these deposits. An old landfill pit underlies most of the toe platform. Riprap has been placed at the landslide toe to prevent landfill material from washing into the ocean (Palmer).

Continual fault activity, erosion, and slumping have made large composite landslides in the Merced Formation. The toes, bodies, scarps, and crowns of these landslides show evidence of recent and continued slumping. Almost every human enterprise above the slide area is threatened: a tunnel, the Ocean Shore Railroad, Coastal Highway 1, and an ever-increasing number of houses (Palmer).





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