Cobbles, Carpinteria State Beach, California


ID 869

Cobbles of Tertiary sandstone embedded in a natural asphalt seep at Carpinteria State Beach in Santa Barbara County. The Miocene Monterey Formation, the source rock for the petroleum hydrocarbons, was deposited in distal marine basins. The sediments (up to 27% total organic carbon) included tests of foraminifera, calcareous nannoplankton, diatoms, and radiolarians. During burial to a depth of 15,000 feet or more, the organic matter was converted to petroleum hydrocarbons. The petroleum hydrocarbons seep out of fractures and naturally flow onto the beach.

In the late 1700ís, the Spanish named this area La Carpinteria, "The Carpenter Shop," because of the woodworking abilities of the local Chumash Indians. The Indians dug pits and used asphalt seeping out of the cliffs to caulk and waterproof their sea-going canoes for transportation to the Channel Islands.


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