Franciscan Geologic Formation at Knowland Park

By Birute Skurdenis

“To look at the geology of Oakland is to look at the geology of California and the planet.” A group of Wild Oaklanders was standing in the shade of an old oak listening to Andrew Alden, geologist, talk about the geology of Knowland Park. Standing on a large flat knoll at the southern end of the park, we were rewarded with sweeping views of the East Bay with San Francisco and the Peninsula in the distance.

An unusual flat knoll at Knowland Park. Photo: Constance Taylor

An unusual flat knoll at Knowland Park. Photo: Constance Taylor

Knowland Park is one of those rare urban places not covered with homes and concrete, where it’s possible to see relatively undisturbed landscape. Most of Oakland consists of ridges, so this flat knoll is a mystery that geologists have pondered but have never come up with a complete explanation for why it’s here.

We were standing on the Franciscan formation, a geological term for the mixture of oceanic rocks found along the California coast and especially in the San Francisco Bay Area. Franciscan formation rocks were churned in the ocean trench where the Pacific Plate meets the North American plate. They were added to the North American continent by the motion of plate tectonics, the same motion that bring us earthquakes along the San Andrea and Hayward faults. We couldn’t see most of the rock underneath our feet because of the dirt covering it, but Andrew introduced us to “knockers.” These above ground rock formations are larger than boulders, which Andrew likened to “plums in the pudding of the landscape.” In the case of Knowland Park, the pudding is a mix of fine grained shale and sandstone. While some of the rocks of Oakland originated 150 million years ago (you can find them in the Leona Quarry area and in other parts of Knowland Park,) the rocks here were only about 60 million years old.

 

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Three knockers at Knowland Park.  The last formation is one that "geology students usually have to travel miles and miles to find- it's pristine! No construction scarring, no graffitti- it's very unusual to find an outcropping that's this undamaged", says Alden. Photo: Constane Taylor

Three knockers at Knowland Park. The last formation is one that “geology students usually have to travel miles and miles to find- it’s pristine! No construction scarring, no graffitti- it’s very unusual to find an outcropping that’s this undamaged”, says Alden. Photo: Constance Taylor

 

The Oakland hills are dotted with old quarries, created by mining materials for road beds and land fill. I find it fascinating to think that the site of Bishop O’Dowd High School, Head Royce School and the 51st and Broadway shopping center are all old quarries.

From the top of Knowland Park, Andrew pointed out where the Hayward fault lies at the foot of the hills, cutting through the Knowland Park Zoo parking lot and extending north through the UC Berkeley campus and into the Bay at Point Pinole.

Being among Wild Oaklanders has the added benefit of being among knowledgeable nature lovers. Members of the California Native Plant Society talked about the Park holding remnants of Bay Area Prairie while other Wild Oaklanders filled people in about the Oakland Zoo’s expansion from its historic position below, near Highway 580, to the ridge near where we stood.

Easy access to Knowland Park is at the end of cul de sacs off Malcolm Avenue. Most have small parking areas and paths into the Park.

People who are interested in learning more about the geology of Oakland should check out Andrew Alden’s blog https://oaklandgeology.wordpress.com and Doris Sloane’s excellent Geology of the San Francisco Bay Region, which is available from UC Press and can be ordered at your local bookstore.

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