Ophiolites
Ophiolite will not
be found in a dictionary of geology before about 1970. Neither
will the term "tectonic plate." Both words describe phenomena
that only recently have been associated with the theory of plate
tectonics, which postulates that land masses and mountains are the
result of movement and deformation of massive plates, or segments
of the earth's crust, which are literally floating atop the liquid
interior of the planet. As molten material flows out of the core
from under the oceans it spreads out and away to finally plunge
back into the earth's mantle. The downward plunging point is
called a subduction
zone -- which just happens to be the location of most
of the coast of California.
An ophiolite is a sort of tectonic
leftover, a sandwich if you will, made up of the lowest layers of
seafloor sediments that have been scraped off in the subduction
zone to be deposited on land. These tasty geologic tidbits are
extremely rare but some geologic gourmand poking around the
cliffs of the San Louis Obispo County coast near Point Buchon
discovered an unusual layering of augite, analcite, calcic
feldspar, and iron oxide minerals, and figured out that they had
slid all the way from the mid-Pacific Ocean to the golden coast
in something over a hundred million years.