Clue: Find the three serpentinite rocks.
Underneath your feet and for miles around are broad bands of a transitional rock that lies between the layered Great Valley Sequence sandstone to the east and the jumbled up, rabble-rousing Franciscan Formation to the west. This rock type that is almost always between the two is serpentinite. Serpentinite is the California official State Rock.
Serpentinite is a transformed version of the basement rock of the earth, far below the ocean floor. The earth’s crust under the oceans is made up of sediment lying on top of volcanic basalt rock, that, in turn, sits on top of its intrusive form, gabbro. Below all of that lies the heavy peridotite, another intrusive rock. The upper levels of peridotite become exposed to ocean water at the mid-ocean rift zones causing this very hard rock to change into the weaker serpentinite. It is sometimes called soapstone and it feels kind of like soap to the touch.
Some sections of ocean floor, known as the ophiolite sequence, were scraped onto the continental shelf as the Pacific Plate subducted under the North American Plate. This is the only method by which this heavy basement rock can be brought up from the depths. During this process serpentinite squeezed its way between the jumbled Franciscan rock and the untouched layered rocks of the Great Valley Sequence.
This transition zone is one of CalTran’s least favorites. Serpentinite is closely fractured and prone to slumping and sliding. Over the past decade millions of dollars have been spent reshaping the angles of repose in the serpentinite cuts along Highway 20. The fresh cuts make the greenish colored rock obvious.
From the cache site you can see a small exposure of serpentinite in the road cut across the highway. Notice that the vegetation is chaparral with a fine sprinkling of digger pines. Serpentinite makes poor soils.
This cache is not on private property so no fence climbing is necessary. Please keep the container well concealed because I'm sure people walk up this far. The clue above should insure success.
Need Cache - Will Travel