The seven stations of the Hayward fault

24 December 2018

Of all the East Bay cities, Oakland owns the longest stretch of the Hayward fault. In my very second post, back in 2007, I suggested that we take over the name, and a couple years back I pointed out eight iconic places to see the Oakland fault in action. To those who still can’t get enough of this amazing geologic feature, this post’s for you.

There are seven places in Oakland where alignments of markers are laid out across the fault trace. These are measured regularly by a team of scientists from the San Francisco State University Fault Creep Monitoring Project using a high-precision theodolite — an electonic gizmo mounted on a surveyor’s tripod. After my last post, I visited all seven places. Let me show them to you, north to south.

Lake Temescal

This line runs along Broadway as it passes Lake Temescal Regional Park. The signs of the fault here (unlike the beautifully cracked sidewalk next to the park staff building) are subtle, and I’ve never felt confident of the exact trace. Nor are there definitive markers. This nail in the concrete is the best candidate, across from the park entrance.

Each alignment station is supposed to have three markers, but I was happy to find even one. It’s probably just as well they aren’t obvious, or people might mess with them.

What they do with the marks is carefully measure the angles between them, then use the data to calculate how much creep movement has occurred along the fault since the crew’s last visit. At this station, creep has measured 4.2 millimeters per year since 1974.

LaSalle Avenue

The fault runs through the heart of Montclair Village, and a set of markers has been measured there since 1993. I don’t know exactly where they are. US Geological Survey Open-File Report 2009-1119 lists locations that are precise to a ten-thousandth of a degree, but they aren’t obvious at all in Google Maps because the precision of the maps is poor. Besides, the traffic on LaSalle was terrible when I visited. (Clearly the solution is to use my smartphone’s GPS capability, so I should get up to speed with that.)

The other thing is that there are lots of things in the street that could be used, like this longstanding fixture.

But even without the markers, the fault itself is evident where the sidewalk has been warped over the years. This view is looking up the north side of the street where the curb has been slowly distorted, the near side creeping leftward by 4.6 millimeters per year.

If there weren’t so many furschlugginer cars and stuff in the way, you could see these features more easily.

Lincoln Avenue

This site has been visited since 1970, the longest-running series of creep measurements in Oakland. It’s at the entrance to the LDS Temple complex, and the fault regularly cracks the pavement next to the Stake Center at the east edge of the property, on its way to the London Road landslide site. This little thing at the head of Maiden Lane might be one of the marks. It certainly looks old enough.

Other possibilities include this unobtrusive saw cut.

Or this more prominent mark.

But you know, all kinds of people have precision business on the ground — utilities, builders and so on. It really sinks in once you start closely inspecting the places you visit every day. And unlike the beautiful brass USGS benchmarks you may have seen, the markers used by the scientists who survey the fault don’t need to be fancy at all. Creep at this location averages 3.8 millimeters per year.

39th Avenue

I’ve featured this location before (twice, in fact), but this time I found the fine little marker shown at the top of this post.

Notice the circle of greenish spray paint around the marker. You’ll see it more in the following stations.

While I was there, I updated my shot of the sawcut in the curb. It’s continued to move, though not at the 4.1 millimeters-per-year pace of the fault as a whole. Creep displacement usually takes place across a wider zone measured in meters, not a single crack.

Maybe in years to come it will be as famous as the Rose/Prospect corner in Hayward once was.

73rd Avenue

This station is at the tight hook in the road where 73rd tops Millsmont ridge and becomes Sunkist Drive for one block. Like the LaSalle station, it was started in 1993.

This marker looked promising, but it’s stamped “EBMUD Survey Control.”

I think this is the real one; note the green paint.

This site has been off my radar as a creep locality, but it has possibilities. The cracks here in 73rd Avenue may resolve into a definite fault trace, if the city doesn’t pave it all over first.

Creep here has averaged 3.4 millimeters per year.

Encina Way

Measurements began on Encina Way, just north of I-580 off Golf Links Road, in 1989. I’ve taken groups here to show them the offset curbs, which are easy to see.

But I had never sought out the creep stations. A splotch of green paint led me to this elegant little bronze dome nestled up at the curb, the size of a half-dollar, with a dent at its center.

Creep here has averaged 3.3 millimeters per year.

Chabot Park

Yes, Chabot Park is run by the City of San Leandro, but it sits inside the Oakland city boundary. Nine years ago I made note of a long row of spikes driven into the road up to the dam. I assume that was the original line established in 1993. It’s much more elaborate a setup than is needed for a simple creep measurement. Perhaps it was a master’s project aimed at measuring the details of the wider active trace of the fault; perhaps it was something else entirely. All I know is that earlier this month I revisited the park and saw the road had been repaved, erasing all sign of the spikes. I did see this nail, though, and there’s the telltale paint too.

Creep here has averaged 4.0 millimeters per year.

Finally, here’s a portion of a cool graphic in the USGS report (800 x 500 pixels) showing the motion measured at these seven stations.

It shows the variations that affect the data — some from the annual wet/dry climate cycle, some from the fault itself — and the effect of our largest local earthquake, the 4.2 shaker of 20 July 2007. The report gets updated, so check it once this post starts getting old.

Posted in The Hayward fault | 1 Comment »

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.

Posted in Franciscan rocks | 7 Comments »

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.

Posted in Oakland streams and water | 3 Comments »

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.

Posted in Oakland hazards, Other topics | 2 Comments »

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