According to the PlateTectonics 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 line dividing the Pacific and North American Plates.
John McPhee, in his Assembling California, described our California fault zones as a twisted rope, roiled and coiled from seafloor spreading that “stitched” material against the Continent. We have many active faults Southern California.
This Earthcache points to one such fault line visible in a hillside cut. Two formations converge in the active Rose Canyon fault line. This California coastal fault is credited with rising (by 400 feet) San Diego’s Point Loma (the farthest point you can get in a southwesterly direction on the North American Continent) and Mount Soledad, looming above La Jolla (pronounced La Hoya, if you didn’t already know). Nestled between are the lowlands of Mission Bay and SeaWorld. This virtual cache takes you to the convergence of two distinctly different geological formations on each side of the Rose Canyon fault. Sandstone laid down fifty million years ago during the Eocene period is faulting up and bumping into a mixture of material, known as Conglomerate, deposited here in the Pleistocene era half a million years ago.
The Rose Canyon Fault (running through San Diego Bay, along Rose Canyon and out to sea above La Jolla) is believed to be on a 350-year cycle for major shifting along this strike-slip fault. The last major movement was 220 years ago as estimated by seismologists.
To log this virtual Earthcache, e-mail me the name of the sandstone formation inland from the fault line.
References: McPhee, John, Assembling California, Farrar Straus and Giroux, New York, 1993 Abbott, Patrick L., The Rise and Fall of San Diego. Sunbelt Publications, San Diego, 1999. Any of the “Roadside Geology” books explaining the roadside cuts and the formations they expose.