The lavas of Easter Hill

10 December 2018

It all started in the Oakland History group, on Facebook, when someone posted an image from a glass-plate negative for sale on eBay: a road-building crew at work somewhere in the East Bay hills. Was it Oakland?

We quickly determined the view overlooked the area that would become Richmond, but what was that little round hill in the rear center? It was too large and rounded to be a shellmound. It must have been bedrock; however, modern maps show nothing like it. But Andrew Lawson’s geologic map of 1913 did — an outlier of Franciscan lava at a locality named Cerrito.

The 2000 geologic map shows it too. Incidentally, I love the old map because it shows that Potrero San Pablo, the rocky ridge on Richmond’s west side, was essentially an island a hundred years ago.

The handsome little hill of Cerrito was called Easter Hill, because it was popular for Easter sunrise services once upon a time. Photos in Calisphere’s Richmond Local History Photograph Collection show it in about 1910:

and in 1912, behind the Stauffer Chemical Company plant, which used to process sulfur-bearing ore from mines in the Oakland hills:

The hill was laid out with roads and called El Cerrito Terrace at the time, but apparently never got more than partially settled before the World War II years because the Kaiser industrial combine acquired it for a quarry, to help fill in the marsh and build the tremendous shipyards of Richmond.

And that was pretty much the end of Easter Hill the hill, but in the 1950s the site became a pathbreaking low-income housing development, Easter Hill Village. After a few decades the neighborhood had gone sour and the buildings had deteriorated, but in the early 2000s Richmond renovated part of it, added new small multifamily homes and renamed it Richmond Village.

I had to go see if the rocks were still there. They are! Take the 23rd Street exit from 580 west and go right on Cutting Boulevard for two blocks, then right on South 26th Street.

Remnants of the hill add topographic interest to the site, and large boulders from the old quarry are placed all around.

Those boulders display a variety of igneous textures and rock types that’s remarkable in an exposure so small. There’s fine-grained, vesiculated (bubbly) andesite.

There’s lava jammed with centimeter-sized feldspar crystals (phenocrysts).

There’s lava ground into fragments by movements of the hot lava around it (autobreccia) — actually two kinds of autobreccia, hot and cold.

I wasn’t sure that all of these came from the same body of rock until I saw them all in one place, packed cheek by jowl in the same outcrop.

But wait there’s more — a textbook-quality outcrop of pillow lava.

Close up, the pillows look almost as fresh as the day they squeezed their way red-hot onto the seafloor and froze in this distinctive form, the outcome of cold water playing whack-a-mole with rising lava.

If you make your way to the hilltop, the rock is kind of punky but the views are inspiring whether you’re looking west, southeast or southwest.

So Easter Hill is still an excellent place to geologize. The village seems like a good place to live, too.

Stream surgery in Dimond Canyon

26 November 2018

Last week was a treat, as the long-awaited start of the annual rains cleared away the thick smoke from the distant Camp Fire. On Tuesday, the air still smoky, I took an afternoon to check in on a few of our streams at their dry-season minimum. Then on Saturday I came back. In Dimond Canyon Park, the new improved Sausal Creek was especially impressive in its reawakening.

In truth, it was never asleep. We did cosmetic surgery on it without anesthesia. Now, as the rainy season proceeds, we need to watch the bandages.

Sausal Creek has had a lot of work done in Dimond Park. The streambed in the park proper, west of the swimming pool, was cleaned out in 2015 and planted in willows — fitting for a creek of its name. In just two rainy seasons, they’ve grown at a prodigious rate.

Now the stream is mostly hidden, but that’s good. To be pleasing for fish, the water needs shade — that keeps the water cool, able to hold more oxygen — and the new thicket keeps out most of the people and their dogs (although I did see a housecat perched on the rocks).

On Tuesday there was precious little water there. It was like everything was holding its breath.

Saturday I could hear the water long before I saw it. A wonderful sound. Even the sterile new section, built after daylighting a stretch that was culverted in 1952, felt like it was ready to burgeon.

Here, just downstream from El Centro Avenue, I could walk up the streambed on Tuesday. . .

. . . but not on Saturday.

The latest surgery is higher up the stream, in Dimond Canyon proper. It involves three watershed wounds, carved by undesirable runoff from the streets around the canyon. Too much sediment washes into the creek for the rainbow trout who live there (I had no idea they’d survived all this time).

Remediating the effects of heavy runoff isn’t a job done by eyeball with a shovel and wheelbarrow. It’s work that calls for heavy equipment, done with surgical care and designed by geotechnical pros. It’s supposed to last as long as the land itself. It’s supposed to heal over with real vegetation and fool the wildlife.

At this site, the object is to keep runoff from carving a gully down the slope. When runoff is modest, it can soak through the channels of stones at the top left and trickle downhill gradually. In a heavier rainstorm, the channels will guide the water aside instead of dumping it all straight down.

The ground is covered with geofabric, a coarse burlap, and strewn with seeds ready to sprout and offer the slope more protection. More substantial native plants, like dogwood, will be added.

The most ambitious part of the project gave a makeover to a long gully reaching the creek from a street drain on San Luis Avenue. This is just the bottom end, below the Old Cañon Trail.

It was ugly. Now it’s raw — the work was finished in September. But it held up fine during last week’s rain, so far so good. The snag of tree roots in the front is meant to be there; dead wood is part of a thriving ecosystem. More shrubs will go along the streambanks where the stakes are.

This site is where the most hard-core work was done. A storm drain from the end of Benevides Avenue unavoidably dumps a lot of water here, so the site is strongly fortified without turning it into concrete.

The plastic pipe directs the runoff onto an energy-dispersing boulder pile. The pipe can be repaired as needed without tearing up the rest of the slope. And if you look closely you’ll see thin sticks standing around the outlet. Those whips are going to grow into trees.

On Saturday this too was a cheerful scene. Some of the whips are already showing leaves.

Over the next few years, let’s watch as the creekside patiently recovers. News, background info and opportunities for the public to help are all at sausalcreek.org.

GHADs—peculiar agencies that safeguard the land

12 November 2018

It’s been a couple years since I’ve visited and written about the Leona Quarry site. It continues to fill with houses. The plantings of local plant species are doing OK, though they’d be happier without the drought. Here’s an updated view from Burckhalter Park, which I’ve visited occasionally since 2003 just for this purpose. (The trees keep getting taller.)

The highest and final residential level, Skyview Drive, is being populated now. The rest of the land will always be open space.

However, the land won’t be exactly natural. It will be intensively maintained. That sturdy concrete flume in the foreground, for example, is there so rainwater runoff from the slopes won’t start digging gullies. The runoff goes to a collection basin at the bottom of the slope that keeps all the muddy sediment and sends the water on into Chimes Creek.

Here’s more of that impressive drainage system, on a lower slope.

What about that high rock face standing in the back? Even from this distance, it looks a little ragged, a little menacing. During my last visit, in January 2016, I was up there and it looked like this.

That crumbling rock was pouring past this temporary barrier and overfilling one of those handsome concrete troughs.

It’s a big and constant job to maintain this infrastructure. There’s always something to do. Who does it, and what happens when something major happens, like a landslide?

In developments like these, a homeowners association typically handles repairs and upkeep for community amenities like paving, play equipment and landscaping. Those aren’t demanding tasks. But what do most homeowners know about geology? For the special hazards posed by geological forces, like erosion and landslides, there’s something better: a Geologic Hazard Abatement District or GHAD.

GHADs (pronounced like “gadzooks” without the zook) are peculiar entities, created under the Beverly Act of 1979, that are set up to handle the specialized job of dealing with geologic hazards for a specific set of landowners. Formally political divisions of the state independent of cities and counties, they’re exempt from bureaucratic headaches like reviews under the California Environmental Quality Act (CEQA) or hassles with the county’s LAFCO agency (and its wretched website). They have elected Boards of Directors and can own land, impose taxes, issue bonds, exercise eminent domain and possess other superpowers. There are dozens of GHADs now, and Alameda and Contra Costa Counties are their epicenter.

What keeps GHADs from running amuck or shirking their job is their “constitution,” a detailed Plan of Control drawn up by a licensed engineering geologist that ensures the Board will act with a prudent level of care. The program of regular monitoring and maintenance is spelled out in an Engineer’s Report, prepared by a licensed geotechnical engineer. It’s a simple but powerful program that spares taxpayers the geological risk inherent in developing sites like Leona Quarry. Learn more from the California Association of GHADs.

The Leona Quarry GHAD was formed in 2005, and by now it has saved up several million dollars of landowners’ assessments for maintaining the defenses — the retaining walls, drainage facilities, native plants and so on — and for major incidents like slides, wildfires and washouts. In emergencies, the GHAD can act with funding in place, trusted experts (from ENGEO) in charge and minimal red tape.

As spelled out in the Engineer’s Report, the concrete drains are cleaned and inspected four times a year, and checked whenever rainfall exceeds an inch in 12 hours. The collection basin is mucked out whenever it fills to a certain level, and the vegetation inside is cut low whenever it grows above 5 feet high. When a wildfire swept over the north end of the upper slope last year, the GHAD sent its plant specialist out afterward to keep the native habitat in good shape, which in turn helps stabilize the slope.

A second GHAD, the Oakland Area GHAD, was established in 2006 for the small Siena Hill development off Keller Avenue. You’ve seen its rugged retaining walls with the fake-stone finish looming as you head east up Keller from Mountain Boulevard toward Sequoyah Community Church.

The builders and the city probably wouldn’t have developed this daunting location without a GHAD that enabled the homeowners to cover their own risk. And now the residents pay their annual fee of about $1500 and the City Council, meeting as the GHAD Board of Directors, spends literally three minutes a year passing a budget and keeping its hands clean of liability. Success for the developers is not certain, though, with fewer than half the lots filled after 12 years.

However, neither has failure been declared. What’s there so far looks really nice.

And from my point of view Siena Hill is a success because it exposes the Leona volcanics well, like this pretty boulder at the far end of Siena Drive.

Farther up is a fresh roadcut that displays the chaotic nature of this intriguing geologic unit, which represents a volcanic island arc of Jurassic age.

The whole thing consists of the distinctive greenish celadonite-bearing phase that I’ve found scattered all over the East Oakland hills. This is the first proper outcrop of it I’ve seen. Well worth a visit.

But enough of this stone cheesecake.

The Oakland Area GHAD is more than just a minor political curiosity; it was established with an eye toward folding in other similar developments as they come up. And it will hit the big time as the Oak Knoll development takes place over the next decade, because a whole bunch of land there, including the open space, the oak woodlands and the streambed of Rifle Range Creek, will come under the GHAD’s purview. The City Council may have to take a few more minutes from now on to manage that.

Work at Oak Knoll began in September. I am looking forward to the day when that land opens up to visitors.

The landslides of London Road

29 October 2018

I spent some time last week in a concerted effort to examine the site of the 1970 London Road/Wilshire Heights landslide. (It took me five years to return to this haunted scene!) The effort was fun, but I learned more at home than I did on site. Gather round the campfire and I’ll tell you the whole tale.

To start with, here’s the most visible sign of this notorious event: the missing side of Kitchener Court, a hard-to-get-to cul-de-sac just south of the LDS Temple parking lot. I took this shot through a chainlink fence as a lone crow cawed.

Deep in the night, the land on the left side, along with its houses, fell into the narrow headwater valley of Peralta Creek, where it pushed a row of recently built homes off their foundations down below on London Road. To orient ourselves, here’s a time series of road maps with London Road in the center. Click it to see its full 1300-pixel width.

Today the whole south end of London Road is gone, except for a tiny stub at the top of Maple Avenue. The north end, of later vintage, extends south from Maiden Lane. The 2018 map, from Google Maps with terrain visible, shows the topographic setting well.

Once upon a time London Road ran up a steep, secluded little wooded valley. It was platted in 1923 as part of the Wilshire Heights development and named for Jack London. It was built out by the late 1950s, after surges of homebuilding in the 1920s and 1940s. Meanwhile, East Bay MUD put water and sewer lines through, and Shell Oil emplaced a fuel pipeline down the valley to carry gasoline from its Martinez refinery to the Oakland Airport.

What could go wrong? A lot. Every steep headwater stream in the Oakland hills is prone to landslides. And this particular stream has carved its charming valley into the pulverized rock along the Hayward fault. Here’s what that shattered, highly weathered material — fault gouge — looks like where it’s exposed in the headscarp.

It was mid-February in 1962, on a dark and stormy night, when the combination of heavy rainfall and leakage from a broken water main caused the hillside just south of Maiden Lane to fail. Three homes were destroyed, never to be rebuilt.

Who knows how long the main had been leaking, or why. Slow landslides could have broken the main, or steady creep along the fault. Either would suffice, but probably both took part. On top of that, literally, was the added load on the hillslope from the new homes and their construction. No ordinances were in place at the time to ensure good construction practices on unstable slopes. And of course, for their landscaping, homeowners just added water. The land was probably in motion long before it finally slid.

Then came more construction in the 1960s: the Warren Freeway on one side, the LDS Temple complex on the other. People in the neighborhood said they noticed new ground movements during those years, but no cause-and-effect relationship can be confirmed this many years later. It is true, though, that when the Mormons sculpted the hilltop for their temple they disturbed an underground realm of water and soil. This photo shows groundwater coming up through the parking lot pavement, a phenomenon people described as the emergence of “hidden springs.”

But for the catastrophe that followed, the unregulated 1920s-era homebuilding on the bluffs of Kitchener Court was cause enough. During heavy rains in early January 1970, the whole east side of Kitchener Court began to collapse onto the south end of London Road. Within two weeks, some 40 houses were affected as 15 acres of land turned to hummocky ruin. The pipeline full of gasoline held, but Shell shut the whole thing down shortly thereafter. (In March 1969 it had been blown up, down in Redwood Canyon, engulfing the village of Canyon in a horrendous fire. Then this. And opposition continued to grow until the bad idea was safely dead.)

This land at the very end of Jordan Road is still iffy after almost 50 years.

There’s also the rock — you knew I’d get around to that. I don’t quite trust the geologic map in this area, but I can attest that serpentinite occurs here as it does in many places along California’s faults. These two specimens are good examples of our typical mixed serpentine rock and blueschist, and large boulders or outcrops of the same are visible in several places. There’s more on the west side of the temple. Serpentinite makes slide-prone ground, too, even when it’s not steep or waterlogged as this place was.

But on the whole, my poking around was frustrating because the land is so heavily overgrown and fenced off. Fortunately the US Geological Survey got funding for a lidar survey of the whole San Andreas fault system, including the Hayward fault, and the processed data — a digital elevation model or DEM, available from OpenTopography — is a fabulous resource for this exact area. After subtracting the vegetation and the structures from the data, the DEM becomes a grayscale image representing the bare ground, with the ghosts of streets and houses, here computer-illuminated from due northwest.

What’s handier, here’s the same with the Hayward fault superimposed. I usually have to do a lot of talking and armwaving to explain things, but not this time. Click in and wander around. The blue outline signifies a sag basin.

My final piece is this closeup of the slide area along with the lot lines and rights of way — more ghosts, still there after all these years.

There’s just one little house left on the east side of Kitchener Court, right up against the temple property. Incredible as it may seem, the adjoining lot, half fallen downhill with cliffs all around it, has a For Sale sign posted. Talk about a haunted place!