Oakland Geology

Oakland’s shore is not what it used to be, not at all. The only hint of how it was is Arrowhead Marsh, part of the Martin Luther King Shoreline Park: a broad wetland laced with tidal creeks and vegetation for all gradations of water from fresh to salt.

And yet even Arrowhead Marsh is reputed to be an accident, formed when Anthony Chabot’s dam, under construction in the hills, had a failure that washed huge amounts of sediment down San Leandro Creek. To fans of nature this history, true or not, is scant comfort.

The geologic map (in this case the map of non-bedrock deposits in USGS Open-file Report 2006-1307) shows that every foot of Oakland’s original shore has been erased and built upon, with the small possible exception of the western tip of Adams Point.

Radio Beach at Oakland’s north edge, our nearest thing to a natural beach, exists on landfill.

Everything in the Oakland Harbor complex, from the Outer Harbor to the military grounds to the airport, is on landfill — “made land” as the old-timers called it.

Coast Guard Island is an artificial pile of Bay sediment, built with dredging spoils.

Alameda doubled its land area by dredging and piling. It’s all there on the map.

East Creek Point, the little peninsula of made land directly east of Alameda on the shore of San Leandro Bay, is a good place to contemplate this great undertaking, its aftermath and its possible futures.

Sitting here in 1852, when Oakland was first incorporated, this scene was a luxuriant marsh like that shown in the 1857 Bache map of San Antonio Creek where the Harbor is today. (The photos in this post are extra big, so click for the full experience.)

From here the view shows nothing of what once was, other than the water and the distant mountains across the Bay. The scene was a planar surface of green and blue, with added brown mudflats at low tide. There were no sharp lines between land and sea; none of the trees on the Corica Park golf course or anywhere else on Bay Farm Island; no brown hill covering a former landfill; no palms and wharves and homes — no ground at all — on the Alameda side; no riprap boulders on this side.

All the land in this view is “reclaimed” from marsh or built outright. Sandy mud was dug up from the Bay floor, crushed rock freighted down from quarries, sand and gravel carried in from excavations elsewhere, construction waste dumped on the shore. Trenches drained the marshes, removing the water to create low-lying land for development.

Even much of the water is artificial, in that it exists by virtue of dredging the Tidal Canal. From initial planning to dedication, the massive project took 28 years, every dollar intermittently funded by Congress. Here’s the canal’s east end from the High Street Bridge. An extension dug across San Leandro Bay is called Airport Channel.

Like the rest of the shore, the canal is heavily armored from end to end.

But what we have reclaimed, nature works to claim back. Around the bend from East Creek Point, the gentle Bay surf winnows out the finer grit and exposes the construction debris holding up the weedy shoreland.

The made land is wearing down, and rising sea level will accelerate the decay. There are two ways to deal with that, and both will be used as the century proceeds: more armoring, and returning the sharp shoreline to gentle transitional marsh. This restored marsh is a start. Similar projects are under way in Alameda, especially in the former military zones.

The “made water,” for its part, is filling up. The harbor needs regular dredging to stay open. That will never end as long as water flows and sediment is carried to the sea.

Finally, the made land is prone to its own problems. In this example near the west end of the High Street Bridge, the ground has settled around the water main in the last 80-plus years. Eventually something will need to be done.

It turns out that the Tidal Canal didn’t work as planned. It was supposed to allow the tide to flush through the Estuary and save the work of dredging the ship channels. That didn’t happen, but now we can’t fill it back up. What an alternate history we would have if it hadn’t been built.

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