The United States Geological Survey is mapping some of the California tar sand deposits that may be suitable for large-scale surface mining. It is contemplated that in some

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cases the bitumen may be removed and treated to yield fuel oil or other products. This paper, however, does not attempt to appraise the economic possibilities of the deposits.

In the several areas mapped to date, the Monterey shale (Miocene) is present and is considered the source of hydrocarbons.

In the McKittrick district bituminous sandstones occur in the lower part of the Tulare formation (Pliocene and Pleistocene (?)). This formation also contains small asphaltite veins. The Tulare is strongly deformed in a broken anticlinorium with a core of Monterey shale. Asphalt oozes from the Monterey and also from tar sands of the Tulare. Some adjacent alluvium is also soaked with tar.

Near Maricopa there are three areas in which asphalt issues from the vicinity of an inclined unconformity between Monterey shale and overlying beds of either the San Joaquin or Tulare formation. Adjacent sandstone and alluvium have locally been impregnated with bitumen.

In the Edna region the Monterey is overlain by shale, sandstone, and conglomerate of the Pismo formation (Miocene-Pliocene). Large, irregular masses of the sandstone are bituminous. They occur on both limbs of a broad syncline which shows subsidiary folds. Some of the asphaltic sandstones have gentle dips, are readily accessible, and have very little overburden.

The Santa Cruz bituminous sandstones are nearly horizontal and are found within and beneath the Monterey shale. Some of the rich sandstones are undisturbed beds, but others are clastic dikes.

At Point Arena, tar sands occur interbedded with Monterey shale and shaly sandstone. The bituminous beds are involved in a syncline and dip rather steeply.

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