Oakland Geology

I celebrate and explore Oakland’s low lands in this chapter of Deep Oakland — a part of town that “contributed the most, and gave up the most, in support of Oakland’s development.” This is a strong claim, but hear me out.

The shoreline of Oakland was completely rebuilt in the making of the seaport and the airport by “land reclamation.” That’s the bland name of a herculean, century-long program of digging up the sandy marsh along the San Francisco Bay to create both “made land” and “made water,” transforming an old-growth continuum into a binary state. And the coastal plain of East and North Oakland has been almost fully paved over after the soil was exhausted by farms and orchards that supported a series of major canneries, then given over to railroads, freeways, factories and broad tracts of small houses. That harbor and that fertile plain made Oakland a vigorous, ambitious and proud city.

You probably knew all that, but there’s more. Beneath the flats and shoreline, Oakland found its largest water supply in deep beds of sand and gravel. Those aquifers yielded millions of gallons per day for decades before East Bay MUD was founded, bringing us Sierra Nevada water and rescuing the East Bay from economic strangulation in the drought year of 1929 with barely a week to spare. Between the shore and the flats, our lowlands, more than anything else, made Oakland a great city — and yet their geology is almost invisible now.

That’s OK, because this chapter also goes into what we can’t see but only infer: the intricate layers of sediment that underlie it all. Over the last few million years, as dozens of ice-age cycles repeated and the basin between the East Bay hills and the San Mateo Peninsula slowly dropped, layers of gravel have alternated with layers of clay to create the rich structure of water pockets that supplied Oakland’s homes and industry.

The basin also records different versions of the San Francisco Bay that have existed during the last million years or so. Until recently there was no Golden Gate; instead the Delta drained through a river that ran across the San Mateo Peninsula through Colma, south of San Bruno Mountain. And before that there was no river at all — the Central Valley was an enormous freshwater body geologists have named Lake Clyde.

The flats don’t have the charm they had under the Ohlones, who maintained them as productive marshes and meadows and prairie. The Spanish and Mexicans were content to treat them as livestock range, and the Americans leached wave after wave of profit from them. The flats still have charm, though, as I’ve said here and as I conclude in the book:

their topography, simple as a blank wall and free of bedrock barriers, is what suits them so well for human occupation. The living environment we have built upon the flats echoes the complex geologic structure beneath it. When I take a random walk through any part of the flats, I enjoy the ways the layers of Oakland’s human history, embodied in buildings and street patterns and vegetation of all vintages, sit in companionable contact. And from everywhere below, the Oakland Hills beckon in the changing Bay light.

This entry was posted on 10 October 2022 at 8:01 am and is filed under "Deep Oakland". You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.