Surface tar-sand deposits in California

Tar sand deposits and oil seeps have been known in California for more than a century and were used in the exploration for many of California's largest oil fields. Sixty deposits visited by this writer yielded 24 deposits totaling 5.27 billion barrels of oil in place and another 36 estimated at 1-2 billion barrels each. Total reserves of tar sands in California appear to amount to about 8 billion barrels. Numerous shallow but unquantified deposits have been penetrated by boreholes. Detailed surface mapping is necessary to delimit accurately the tar sand deposits. For example, the Edna deposit, generally credited with 1 billion barrels, actually contains only about 200 million barrels. On the other hand, the Casmalia deposit probably contains more than 1.5 billion barrels.