Oakland Geology

This is an inventory of what’s left of Glen Echo Creek, a stream with an outsized significance in Oakland’s history of development and planning. I used to live in its watershed and retain a strong affection for it. The photos in this post document every bit that’s accessible to the public. But first here’s the watershed map, courtesy of the county flood control district.

I’ll focus on the main branch, labeled “Cemetery Creek” in its upper reach (the Rockridge Branch on its north side is worth its own post). You can see that close to 90 percent of the creek runs underground today in culverts. Cemetery Creek’s headwaters, in Piedmont’s Moraga Canyon, are buried under Blair Park; the creek trickles out below Coaches Field at the edge of Mountain View Cemetery’s property.

From there the water goes through the cemetery’s three little reservoirs. This vintage view over pool number two is from my post celebrating the cemetery as the Bay area’s best landscape.

Once past the cemetery, the stream is known by its developer-inspired name of Glen Echo Creek. The upper portion, shown in this closeup, has four small segments of living water.

The first two are in back yards, and I’ve never seen them. This is the third, a brief flash at the end of tiny Arroyouela Avenue.

The fourth segment is partly public and partly private. The entrance to the Glen Brook Terrace includes two bridges and a sewer line, one of dozens I’m sure.

Just downstream is the narrow preserve, two residential lots wide, named Glen Echo Park. Neighbors help maintain it. The part above Monte Vista Avenue has a bit of the old floodplain. That’s where the stream flowed before white people came in the late 1700s. The disturbances they made to the countryside led all the little streams to cut into their floodplains forming the steep-sided arroyos we know today.

The creek enters a tunnel and comes out a thousand feet away, under I-580. That’s in the lower portion of the map, shown here.

Starting with Frederick Law Olmsted in the 1860s, thought leaders had a vision of the city laced from the shore to the hills by arterial parklike streets along each of the streams. Charles Mulford Robinson, a leading figure in the City Beautiful movement, was all about using our stream valleys for elegant roads with exquisite views.

The planner Werner Hegemann cited that vision in 1915: “A little suggestion of Charles Mulford Robinson’s plans may be found in the charming piece of a drive following for a short distance Glen Echo Creek under the name of Richmond Boulevard; though this has been carelessly handled by crossing the creek in some places by crude solid fills instead of light bridges, the elegance of a drive along a creek bordered by live oaks in contrast to the baseness of the use of the stream as a storm sewer is very convincing.”

It’s hard to square that picture with today’s dark, overgrown Oak Glen Park.

The envisioned road would never serve serious traffic, and the creek is far from a natural stream. Its fortified banks are choked with English ivy, Himalaya blackberry, French broom and other invasives, with no cleansing floods to clear them.

From here the stream runs privately through front yards, then a concrete ditch behind the Grocery Outlet.

The mappers of the flood-control district missed a final exposure, next to 27th Street at the black dot on the map. This is the last place one can hear the water speak.

Still farther downstream, at the second dot on the map, a ghost of the old creek was exposed as construction began at 24th and Harrison. This is the path of a long-disused culvert, being cleaned out and buried last week.

A photo sent by a reader shows details from a few weeks ago.

Finally we have the wholly artificial channel leading to the creek’s mouth at Lake Merritt.

One of Oakland’s great civic failures was its inability to preserve the natural streams. It took seven generations to reach this state, and it will take seven times seven to undo even part of it. Until then, we can only perceive the moribund creek in the topography of its valley, an echo of the glen it left us.

Like all true Oaklanders, I keep coming back to Lake Merritt. In this visit, I’ll muse about the many times in the recent geologic past when there was no Lake Merritt here.

If we assume, as I do, that the uplifted block of bedrock making up most of Lake Merritt’s watershed is about 1 million years old, then this little arm of the Bay has a fairly deep ice age history. A million years rather neatly fits the period of Pleistocene time after the Mid-Pleistocene Transition, when for imperfectly understood reasons glacial cycles changed from roughly 40,000 years to 100,000 years in length.

Let us then stipulate that this part of town has gone through about ten full glacial cycles. Each time the world’s ice sheets and ice caps grew, the sea level fell by a hundred meters or so — three or four hundred feet! Here’s a recently published set of sea level data for the last nine cycles. Various lines of evidence agree, though never in exact detail, about the timing and magnitude of the changes. That’s what paleoclimate science looks like.

^{From Rachel Spratt & Lorraine Lisiecki, 2016, A Late Pleistocene sea level stack, Clim Past 12(4)}

Each time the sea fell, all of San Francisco Bay slowly drained dry and the coastline withdrew out past the Farallon Islands. Every stream that could do so cut into the newly exposed ground, digging gulches, ravines and canyons into the young sediment where before they were prevented by the high sea level. That’s when Lake Merritt became temporarily Merritt Canyon, with Merritt Creek surging along its bottom.

Each time, Merritt Creek dug out all the gravel and mud that had filled the basin of Lake Merritt and shoved it straight out into the Bay, where the drainage ran south and then around the end of San Bruno Mountain into the Pacific. That’s right — the Golden Gate didn’t exist. Instead, the Bay area streams and the great Central Valley rivers drained through what’s called the Colma Gap.

Here’s an illustration from a publication I refer to often, Sandy Figuers’ “Groundwater study and water supply history of the East Bay Plain,” that shows the typical drainage pattern of those times.

^{Courtesy State Water Resources Control Board}

It’s very interesting: the river ran east of the Potrero Hills in Richmond, east of Yerba Buena Island, and all the way down to around San Mateo. And Merritt Creek, right in the center of that map, pushed a big fan of alluvium — river gravel and sand — into the basin that rivaled the fans of the other major East Bay streams. It went right under Alameda. That’s because Alameda wasn’t there.

This configuration of the Bay lasted from about 630,000 years ago, when the great freshwater Lake Clyde that once filled the Central Valley broke through the hills and cut Carquinez Strait, until the last warm interglacial period about 125,000 years ago. The sea at that time rose even higher than it is today, and motion on the San Andreas fault closed the Colma Gap. That’s when another gap opened up farther north on the fault, which became the Golden Gate.

So when the next glacial age began, the whole drainage pattern of the Bay shifted dramatically. Also the winds: instead of blowing south through the Colma Gap, the ice age westerlies carried huge amounts of glacial sand through the Golden Gate and across San Francisco, across the dry grasslands of the Bay and onto the East Bay slopes. That’s when the big fields of sand dunes accumulated in San Francisco and in three places on this side of the Bay: in downtown Oakland, in Alameda and on Bay Farm Island.

The latest time that Merritt Canyon formed, Alameda sat in its way all of a sudden, and I think Merritt Creek must have drained west, down San Antonio Creek (today’s harbor estuary), not southward as shown on this figure from the same report.

Here’s part of a third figure from that report, showing the depth to bedrock in Oakland as determined in boreholes.

Merritt Canyon really stands out underground: over repeated ice-age cycles, as the Bay floor has gradually subsided, the earliest versions of the canyon now lie 600 feet below Lake Merritt.

There should be a record of successive incisions and fillings of the canyon preserved down there. It would take a concerted campaign of core drilling and seismic reflection profiling to map and characterize it, and if I were a billionaire like some people I won’t mention, I’d spend the money even though it would be a huge hassle to get the permits.