Correlates of the Lakeside Park terrace

19 July 2021

The flat ground of Lakeside Park (and also the Clinton neighborhood) is an unusual landform for Oakland and the East Bay in general: it’s a terrace made of gravelly sand and clay that was deposited around 125,000 years ago, a time when the sea level was several meters higher than today. I’ve featured it in previous posts, but today I’ll go farther afield, because the things we know in geology are based on more than just looking at what’s in front of us.

The formal description of this terrace, mapped as unit Qmt, marine terrace deposits, in the geologic map, includes this: “Similar terraces are located north of the map area on the south shore of San Pablo Bay in the extreme northwest Contra Costa County at Lone Tree Point, Wilson Point, and an unnamed outcrop in between. The oyster beds at the base of these outcrops unconformably overlie the Cierbo Sandstone of Miocene age and are in turn overlain by about 5 m of greenish-gray silty mudstone. The oysters have been dated by the uranium-thorium method and are of last interglacial age, approximately 125 ka.” So last week I made a road trip to see these terraces. I also looked into the literature. Both had mixed results.

Unless you live in the Pinole-to-Rodeo corridor, you’ve probably never heard of Wilson Point and Lone Tree Point. Here they are on the 1949 topo map, when the area was much less crowded. Hercules was still a company town, organized around the dynamite works there. (Now the area is being paved with over-the-top condo/townhome developments.)

These days the Bay Trail offers access to most of that stretch of coastline.

I’ve always been curious about these little bits of land along the coast because the Capitol Corridor trains go past them at a relatively slow speed. Wilson Point is on the other side of the tracks, which are fenced off. I must advise you not to cross them.

However, if you choose to ignore my advice, take the trail through the gap in the fence and carefully approach the point. This view shows the underlying rocks, with their tilted beds, and the small remnant of the terrace deposits on top. The difference in angles between the two layers is what “unconformably” refers to in the description.

Here’s the contact between the rock and the terrace deposits. The original source of the description I quoted above (USGS Open-File Report 93-286) clarifies that between the tilted bedrock and the shells is a layer of estuarine mud, the kind of muck you’ll find in a bayside marsh today. And behold, here’s a fine layer of consolidated mud topped by a fine layer of shells. These are the shells that were dated as 125,000 years old.

And above them is this hard gravel cemented with clayey silt. It is very much like the gravel at Lake Merritt: the particles are the same size, rounded to the same extent and similar in the variety of rock types represented in the pebbles.

So this is the evidence used to decide that Oakland’s terraces date from the last major interglacial. Now let’s look at Lone Tree Point, up in Rodeo. When you’re riding the train, it’s where you pass this wrecked boat. Note that the old pier on the left is resting on bedrock.

The train tracks punch through the waist of Lone Tree Point, and a bridge leads over the tracks. You can see those details in this photo. I advise you to take that bridge, which gets you onto the land at the south end where the marine terrace is, which is owned by the East Bay Regional Parks District.

Note the area of rock in the middle. That’s where I took the next photo.

This rock pavement is the hardened ancient Bay mud that was laid down on the surface of tilted rock beds. The terrace behind it preserves it all: bedrock, mud, shells, gravel.

Here’s a more detailed view; click to view its full 1200-pixel splendor.

The story goes like this: in cold glacial times the waves cut a wide flat surface across the tilted bedrock, the kind you’ll see active today along the Pacific coast of San Mateo County. Then the glaciers melted, even much of the Greenland and West Antarctic ice caps, and sea level quickly rose upward several meters higher than today, it was that warm. The bare rock platform collected a coat of Bay mud. Meanwhile streams got busy in the warm, wet climate, and washed huge amounts of gravel down from the hills into the bay, building thick deposits up to the waterline and perhaps above it. The shells got ripped up, tumbled around and somehow laid down first; I’m not clear on just how, but the shells clearly are not lying where they lived. Then the glaciers came back with a vengeance, the sea was drawn down more than a hundred meters, and the terraces were left high and dry and prone to erosion. Only little bits of them are left, especially now that the sea is high again (and rising) and attacking the entire California shoreline.

Now, in the Oakland terraces only the gravel part is visible. Assuming that there’s a shell layer and mud layer and a wave-cut platform beneath the gravel, those must exist a little below sea level. I don’t think we know; I’m not aware of any borehole records from Oakland’s terrace, although there must be some. But the same authors who documented these terraces on San Pablo Bay reported that shells of the same age have been found as deep as 40 meters below sea level in the South Bay.

The implication is that the whole southern part of the San Francisco Bay basin has been sinking while San Pablo Bay has pretty much stayed where it is. That’s what geologists do with a few data points: they make up a plausible story and see if any new evidence fits it. Oakland’s terrace appears to lie between those two levels, so the evidence, such as it is, fits.

I’m skeptical, frankly. The initial layer of mud is said to be 4 meters thick. That’s not true at Wilson Point, and that’s stretching it at Lone Tree Point. Also, the supposed “oyster beds” are a shell hash, not present in all outcrops, in which real oysters appear to be uncommon. Sometimes this happens when you check everything out on the ground.

The HayWired scenario of lost homes

5 July 2021


Soft-story damage in San Francisco’s Marina district, 1989. Retrofit programs in Oakland aim at preventing this kind of destruction.

As you all know, the Hayward fault runs through the middle of Oakland and the whole East Bay, and as you all know it will rupture some day in a large, destructive earthquake — a catastrophe on the scale of the 1906 San Francisco quake and fire, or Hurricane Katrina in New Orleans in 2005.

A large group of researchers led by the U.S. Geological Survey has been working with governments, insurers and others on ways to foresee what the earthquake will do, in hopes we can counteract the worst of it beforehand and cope better with it afterward. Their product is a detailed earthquake scenario, called HayWired, that enables planners of all kinds to work together in a coordinated way and come up with meaningful, actionable recommendations. I’ve been following the effort, and reporting on it here, for four years now.

Last week I checked in on the state of the effort in an online seminar by SPUR, the regional planning nonprofit, titled “Where Is Home after a Large Earthquake in the Bay Area?” (This and previous seminars can be found here.) Prompted by the release of new chapters in volume 3 of the HayWired report, it focused on rebuilding housing after the HayWired quake in the communities most at risk. Forgive the metaphor, but we have to light a fire under all levels of government and keep blowing on it.

The HayWired scenario earthquake is a magnitude-7 event that occurs on an April morning, rupturing the whole northern half of the fault from an initiation point under the Crestmont neighborhood. As the shaking ends, landslides grind their way down hundreds of hillsides, bayside ground turns to soup and almost 500 large fires are triggered. Some 800 people are dead, not counting deaths related to the fires. In the nine-county Bay area, a million buildings are damaged or destroyed. Property losses amount to $40 billion in Alameda County alone. These are the best estimates we know how to make.

That’s all before we get to the local impacts. A belt of badly damaged neighborhoods extends along the fault from Pinole to Fremont plus outliers in Novato, Pleasanton and Vallejo, but the community most at risk is all of East Oakland.

Even when the houses survive, neighborhoods don’t just heal. People will keep leaving heavily damaged areas, in “voluntary displacement,” for three understandable reasons:

1. They can’t afford to stay — their jobs fail, their money runs out, rents rise too high.

2. They can’t stand to stay — roads and transit and water are down for months and perhaps longer; schools and shelters shut down; aftershocks drive them nuts.

3. They don’t have to stay — they’re young, they’re mobile, they’re ready to go somewhere better.

Voluntary displacement was a notable factor after the 1994 Northridge earthquake, when neighborhoods turned into “ghost towns” as people kept moving out, especially where multifamily residences were common. In New Orleans it was even worse. And it will be a big consideration in East Oakland, where so many residents already have “vulnerability factors” like low income, language problems, youth and old age, and lack of education.

I’m almost done with the bad news. Government money will be slow in coming and far short of the need. Earthquake insurance will help individuals who can afford it, but no one will be made whole. And some areas will require a complete makeover, which will take years of planning and be politically fraught.

What can be done to help in advance? We have shoestrings of help like the state government’s earthquake insurance fund. We have the state’s Earthquake Brace + Bolt program that helped pay to strengthen 15,000 dwellings. (Until they announce more funding for 2021 especially for underserved neighborhoods, you can find qualified contractors on their website.) Oakland has a slow-moving mandatory retrofit project aimed at saving our existing housing stock from collapse. Those small-scale programs are laudable, but they won’t cut it.

Speakers at the seminar pointed to larger efforts. On the biggest scale, SPUR issued a report this year on fixing the Bay area’s massive housing problem over the next 50 years. Every new house or apartment is more earthquake-resistant than anything older, which is why I strongly favor housing construction at all scales. I learned the most from Maziar Movassaghi of the state Department of Housing and Community Development, who had hard-won advice from the 2018 Camp Fire disaster. Recovery has taken years because people couldn’t build new multifamily housing until the roads and infrastructure were ready, and then the financing took even longer. The bureaucracy is complicated, the money is tight and it all takes too long for people to endure. And all the while the pressure is to do the easiest thing — build back what used to be there — rather than the resilient thing — build something better.

What Movassaghi recommended was to have plans in place for housing recovery after disasters, the lack of which was a big obstacle after the fires. (He noted a good example from San Jose.) Funding agencies won’t just write a big check — a multiyear community development block grant — if your city can’t show them it knows what it’s doing. Such plans, he said, should be made jointly by community-development folks and emergency-management folks, to make sure the new neighborhood will come through the next disaster better than it did this one. Having good plans in place can save your city years of misery.

For most of us this kind of work is above our pay grade, but it’s within our horizon of concern. We can do what citizens do: listen, learn and lobby our public servants.

Previous posts:

HayWired, an imaginary earthquake coming in 2018

News from the HayWired fault

Earthquake advice for Oaklanders 4: What to do

Mountain View Cemetery’s earthquake plot

21 June 2021

The pandemic has eased enough that Mountain View Cemetery, the Bay area’s finest landscape, has opened its gates again to the public, though only on Wednesdays and Saturdays for the moment and with an earnest plea for your good behavior. Thus on Wednesday I was finally able to visit Plot 1, where the first earthquake victim in the East Bay’s history is buried: Joseph W. Josselyn. It turns out his monument isn’t the only one there with an earthquake connection.

William Halley’s 1876 Centennial Year Book of Alameda County reproduces the account of the great earthquake of 21 October 1868 from the next day’s Oakland News, giving us the picture of Josselyn’s worst day: “At San Leandro the earthquake was much more severe than in Oakland or Alameda, and not a building escaped damage. The saddest calamity was the death of Mr. J. W. Josselyn, Deputy Clerk, a young man of much promise and ability, who has for a few years past been in the office of the County Treasurer. He was crushed in the ruins of the County Court House. . . . There were in the Clerk’s office four persons besides Mr. Josselyn. Mr. Josselyn endeavored to escape by the front entrance to the building, and when passing the threshold the falling walls buried him in its fragments. The other persons, seeing the front give way, escaped through one of the windows.”

The courthouse (San Leandro being the short-lived county seat at the time) was newly built, and the shaking was said to have revealed its shoddy construction. On the other hand, the earthquake broke every chimney in San Leandro that foggy morning, so maybe the fault lay not in the building, but in the Hayward fault. The lesson learned after every major quake is always the same: don’t try to run outside while the ground is shaking. The way we state that lesson today is: Drop, Cover, Hold On.

Halley reported, “The lamented Josselyn’s funeral took place at 11 o’clock on the morning of the 23d of October, from the Presbyterian Church, and under the auspices of the Masonic fraternity. His remains were interred in Mountain View Cemetery, near Oakland, and over eighty carriages formed the funeral procession.” His fellow Masons did well by Josselyn, furnishing his grave with a fine sandstone stele with the Masonic square-and-compass emblem and some skilled carving.

I perceive a message in the emphasis the carver gave the date of Josselyn’s fate. This date was carved into local memory as surely as 17 October 1989 is in our own (in mine, anyway).

Michael Colbruno’s “Mountain View People” blog has a photo of Josselyn that gives a hint of his energy and popularity.

Behind Josselyn’s monument is the white marble stele of the Pardee family plot, one of the handsomest bits of Plot 1 with its upgraded frame of ornamental gravel.

Enoch Pardee, the patriarch, builder of the Pardee mansion, was a major Oakland figure in his time, but his son George, a figure of even greater renown, is the earthquake connection.

George Pardee was born in the earthquake year of 1857 and experienced the 1868 quake as a youth, but it was the 1906 San Francisco earthquake that marked his life the most. He was governor of California at the time, and he immediately took the train to Oakland to oversee the state’s response from his family home. There he welcomed refugees from across the Bay, many of whom stayed in Oakland in a great pulse of population and development.

The 1906 earthquake did much damage in Oakland, by the way, but here in the cemetery, according to Andrew Lawson in the 1908 Report of the State Earthquake Investigation Commission, “the chief damage done was the cracking of the receiving vault, and that was not injured very much. In St. Mary’s Cemetery, on the small ridge to the west, however, many monuments were moved or twisted and several were overthrown.” An observer counted about a dozen monuments disturbed here, mostly by twisting. (Lawson himself was buried at Mountain View in 1952, one of Mountain View’s contingent of noted geologists.)

Bay Farm Island

7 June 2021

The middle East Bay shoreline has three lumps in it, three bodies of ice age sand dunes that would seem more at home in San Francisco than over here. The first, the biggest, underlies downtown Oakland; as the city border signs say, it reaches an elevation of 42 feet right at City Hall. The second underlies Alameda, the former peninsula, and has a maximum elevation of about 35 feet. The third, smallest and lowest of all, barely over 10 feet, an accident of the modern sea level, is Bay Farm Island.

The Ohlone tribes came here to harvest shellfish from the tidal flats and bird eggs from the fields, although they apparently did not stay long or build shellmounds on the place they called Wind Whistle Island. The earliest maps show a small area of treeless land with marsh on three sides and a sandy bluff facing the Bay. This is Captain Beechey’s map, surveyed in the late 1820s.

The first USGS maps, from the late 1890s, accurately show the original island. Note that the marshes drained away from the Bay, a sign that the island formerly extended farther east.

Like Oakland, the land was settled by squatters in the early 1850s, but instead of real-estate speculators they were farmers who quickly spotted the advantages of clean virgin soil, a high water table and easy access to the San Francisco markets. They did so well, this isolated patch got its name almost immediately. Bay Farm Island asparagus was famous — farmers cleared $500 an acre in Gold Rush dollars — and having grown it myself I can see how that crop would thrive in this excellent fine dune sand.

In the 1870s, efforts began to drain the marshes and turn it into hayfields and “made land.” A 1878 map neatly juxtaposes the old property lines on the natural island and the new speculator lots on the reclaimable land around it. The outline of the firm ground was a miniature of the Alameda peninsula, a baby slipper next to its parent as seen in the geologic map.


Thompson & West map, 1878 on davidrumsey.com

Maps from around 1900 show the island divided into large farm lots, with windmill-powered wells and long windbreaks planted against the prevailing northwesterlies. The twentieth century nearly erased all of this geography, as the former marsh was built up into the Oakland Airport, the Corica Park golf course and the Harbor Bay residential and business development. An overlay of the 1878 and current maps shows that there is no natural shoreline left.

Today Shoreline Park, at the western tip of the original island, is a manufactured shore on a high berm, armored with riprap. Inland, high residential walls and mature trees blunt the stiff wind off the Golden Gate.

But the pervasive landscaping and air traffic overhead can’t camouflage its eerie setting, a naked, remote, windswept place in the belly of the Bay.

What might Gertrude Stein, who famously bemoaned the loss of the Oakland she recalled from her youth, have said had she come instead from temporarily Bay Farm Island?

Read an excerpt from Eric Kos and Dennis Evanosky’s book on Bay Farm Island