San Andreas Fault at Alder Creek
February 13, 2007
Near the mouth of Alder Creek at Manchester State Beach in Mendocino County, California, the San Andreas Fault goes offshore. After crossing Pacific Coast Highway (CA-1), it slices northwest through a headland that reveals the fault’s presence in textbook style. Along the fault’s trace (arrows), there's a line of enhanced vegetation that occurs when water flowing underground encounters water-impermeable rock that the fault has shifted across (fault gouge). Unable to continue its down-slope journey through the porous rock, the water is brought to the surface where it irrigates the vegetation along the fault. Also present is the most characteristic aspect of the fault itself: different rocks on either side of the fault. Photo taken in November of 2005.