Oakland’s Varied Geography and Geology.

Have you ever thought about how varied the geography and geology of Oakland is? Let’s consider a few facts.

In terms of area, Oakland spans 78.0 square miles. Did you know that 28% of what is within the boundaries of Oakland (22.2 square miles) is covered by water (e.g., Lake Merritt, Lake Temescal, part of the bay)?

Key changes have occurred in Oakland’s 19 miles of shoreline over the years. This shoreline used to be covered by hundreds of acres of salt marshes and shallow tidelands, providing a natural habitat for many species of fish, birds, mammals, and other forms of wildlife. Dredging and fill during the 20th century for military, port, and commercial activities greatly reduced the quantity and quality of Oakland’s natural shoreline. While efforts have been made to restore some of the natural habitat, much more needs to be done, but that’s a discussion for another day.

I’m curious to know how many Oakland residents have ever been to Radio Beach. Have you ever heard of Radio Beach (neither did I, until yesterday – and now I’ve been there!)? Radio Beach is the only beach in Oakland, located just north of the on-ramp to the Bay Bridge. The beach gets its name from the radio towers located there.

Many fine views of the bay, the bridges, and San Francisco can be found from that 400-foot stretch of sand. The beach is not maintained, so don’t expect to swim or sunbathe there.

Radio Beach

Radio Beach.

About two-thirds of Oakland’s land area is flatland, called alluvial plain. An alluvial plain is formed over a great period of geological time by sediment transported and deposited by ancient waterways. Alluvial soil is geologically unstable. Since so much of Oakland’s population and commerce is located on this alluvial plain, it’s imperative that we take special seismic precautions when constructing buildings.

Which brings us to the Hayward Fault. A fault is a thin zone of crushed rock that separates blocks of the earth’s crust. Earthquakes occur when the blocks move. The Hayward Fault is 74-miles long, running in a southeast to northwest line from San Jose, through Oakland, up into Richmond, and terminating under San Pablo Bay.

In Oakland, the fault runs along the western base of the Oakland Hills. As it goes northwest, the fault runs close to Highway 13 and Mountain Boulevard. As the fault approaches Highway 24, it passes under the eastern side of Lake Temescal, continuing on into Berkeley.

According to the University of California’s Berkeley Seismological Laboratory (BSL), the last major earthquake along the Hayward Fault was in 1868 – 144 years ago. Since the last five major earthquakes along the Hayward Fault occurred, on average, every 140 years, BSL warns that “It is very likely that the Hayward Fault will rupture and produce a significant earthquake within the next 30 years.”

Since we live close to this fault, it would be wise to keep on hand some supplies you might need (e.g., bottled water, canned food, a can opener!, first aid kit, flashlight, fresh batteries), should an earthquake disrupt electrical and water lines or wreak other havoc. You might want to keep your earthquake insurance up to date, too!

Finally, we come to the Oakland Hills (officially, the Berkeley Hills). The highest point in Oakland is 1,760 feet above sea level, just off Grizzly Peak Boulevard. About ten million years ago, these hills included active volcanoes. Today, the active volcanoes are part of our distant past, but their evidence remains in the form of rich lava deposits, thrusts of layered sedimentary rock, and basalt.

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Exposed layers of sedimentary rock in the Oakland Hills.

The Sibley Volcanic Regional Reserve, on Skyline Boulevard in the Oakland Hills, is a great place to hike and learn about the volcanoes that once erupted here, spewing ash and lava all over the area. In fact, Round Top (1,742 feet high), located within the Reserve, is an extinct volcano that’s been tipped on its side by tectonic forces that occurred along the Hayward and neighboring Moraga Faults.

Round Top

Round Top.

That’s a lot of geography and geology to pack into our little 78 square mile community (and a lot to cram into a short blog entry!). Let’s get out and enjoy it today, but also protect and preserve it for tomorrow.

Keeping Oakland Beautiful is everybody’s business.

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