There’s Oil in Them Thar Sea Cliffs!

A sandstone dike that cuts across the Santa Cruz Mudstone. The blue line parallels the dike just above it.
A sandstone dike that cuts across the Santa Cruz Mudstone. The blue line parallels the dike just above it.

If you look in the northern most cove at Bonny Doon Beach, (yes, it’s the clothing-optional section), you will see a tall skinny dike of sandstone that cuts across the cliffs-which are made of Santa Cruz Mudstone. A dike is essentially loose material, in this case, the older and deeper Santa Margarita Sandstone, that was squirted up under pressure through the younger but harder mudstone. The dikes and the Santa Margarita Sandstone in general contain bituminous (asphalt-like) material in varying quantities. There are many similar dikes in the sea cliffs along the north coast of Santa Cruz. This one is unusual in how skinny and rectangular it is.

Bonny Doon Beach.
Bonny Doon Beach.

Some of the bituminous sandstones just a few miles south of Bonny Doon Beach, at Majors Creek, were quarried for paving material. Apparently about 600,000 tons, valued at over 2 million dollars, were quarried and sent by boat to pave San Francisco between 1888 and 1914.

Photo from the collection of Gary Griggs. See his article on these intrusions.
Photo from the collection of Gary Griggs. See his article on these intrusions.

In the 1950s the Husky Oil Company ran an experimental project to get oil and gas out by heating the sandstone in the drill hole and then recovering what melts. Over three years they pulled out 3,000 barrels of oil and some gas. In general, costs were too high to make it economically viable.

Take the Self-Guided Mobile Tour

This piece is part of the North Coast Tour. Download the free app with many tours of the Santa Cruz area and beyond.

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Go to Mobile Ranger Guides in the Apple App Store
Go to Mobile Ranger Guides in the Google Play Store
  1. Sources Used

    • Living With the Changing California Coast. Gary B. Griggs, Kiki Patsch, Lauret E. Savoy. University of California Press; 2005.



About The Author

I really enjoy field trips. I love being in a cool place and having someone tell me about it. The problem is, you can’t always find a professor or park ranger-type to tell you all they know about the local rocks, plants, and history. So I decided to combine my love of things natural with mobile technology.

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