Cape Mendocino

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Cape Mendocino in Humboldt County, California, USA, is the westernmost point on the coast of California. (Mendocino County lies to the south.) It has been a landmark since the 16th century when the Manila Galleons would reach the coast here following the prevailing westerlies all the way across the Pacific, then make their way down the coast all the way to Acapulco, Mexico. Its first lighthouse was lit December 1, 1868, standing on eight prefabricated panels sent up from San Francisco.

The Cape Mendocino region of California's north coast is one of the most seismically active regions in the "Lower Forty-eight" United States. Three earthquakes with epicenters nearby at Petrolia and offshore west of Cape Mendocino, 25–26 April, 1992, were outstanding, one reaching 7.2 on the Richter scale; they demonstrated that the Cascadia subduction zone is both capable of producing large earthquakes and generating tsunamis. Many geologists and seismologists believe that the main shock in the 1992 sequence may be a forerunner of a much more powerful earthquake in the Pacific Northwest.

Just offshore of Cape Mendocino, there is an unstable triple junction where three tectonic plates come together. The San Andreas Fault, a transform boundary, runs south from the junction, separating the Pacific Plate and the North American Plate. To the north lies the Cascadia subduction zone, where the Gorda Plate is being subducted under the margin of the North American plate. Running west from the triple junction is the Mendocino Fracture Zone, the transform boundary between the Gorda Plate and the Pacific Plate.