According to the Plate Tectonics people everything west of the
notorious San Andreas Fault -- the one responsible for major
earthquakes in California including San Francisco's 1906 event --
lies on the Pacific side of the margin dividing the Pacific and
North American Plates. Plate tectonics move the Pacific Plate
northward along the North American Plate at the rate your
fingernails grow. But the major San Andreas Fault landlocks as it
twists and turns through Southern California well inland from our
coastline. It's the build-up and relief of these pressures that
cause earthquakes.
This Earthcache points to one glimpse of the major fault zone
emerging out of the pacific cliffs, on its way along the coast and
out to sea at Eureka, California. Our slip-strike fault in So Cal
gives way to a subduction action in the Pacific Northwest, Canada
and Alaska where the Pacific Plate crust can return to magma,
creating volcanoes (the Ring of Fire) that define its
perimeter.
This virtual cache reveals a major strand of the San Andreas
Fault at the juncture of two major geological formations. Instead
of being side-by-side, as in my Rose Canyon EarthCache (It's Not My
Eathcache Fault CA), these two formations of the San Adreas Fault
zone are more horizontal, with the rock and the mud pushed up from
the ocean floor. According to an article by Dan Sudran (California
Wild's web link below) these two formations are the Francisca
Complex of 80 to 90 MYA and the Merced formation, a sedimentary
formation laid down at the ocean bottom some 3 MYA.
Afternoon is the best time to view these different formations in
the most favorable light. Watch out for hang gliders, parafoils and
RC model airplanes landing on the plateau.
To log this earth cache, e mail the colors and approximate
incline angle of these two geological formations thrust up from the
sea floor along the plate boundary.
References: Hough, Susan Elizabeth Finding Fault in California,
Mountain Press Publishing, Missoula, MT, 2004 McPhee, John,
Assembling California, Farrar Straus and Giroux, New York, 1993
Sudran, Dan, article California Wild
http://www.calacademy.org/calwild/2004winter/stories/closerlook.html