The St. James Drive roadcut

11 December 2017

Recent work in far east Piedmont has exposed some excellent bedrock worth a close inspection. Because the town government won’t put an interpretive sign there, this post will have to do.

To my knowledge, there are only two sites of powerline towers in Piedmont, one at the mouth of Estates Drive and the other at 298 St. James Drive, near Park Boulevard. Last year the power company replaced the latter pair with shiny new towers, and as part of the work it cleared the roadcut of its cover of acacia trees (Google Maps shows the site as a thicket going back to 2007). Shortly afterward I discovered it and had high hopes, though it wasn’t much to look at in late October.

By January, the exposure had been stripped of loose rock. Already it was clear that it would be a showcase of slickensides.

By August, a strong concrete wall had been put in place and landscape plantings made.

The slickensides turned out to be fabulous. These are the polished marks made as movement along faults grinds rocks against each other.

And here’s a closeup.

Also visible is evidence of brecciation, the geologist’s word for shattering rocks and cementing the pieces together.

The rock here is sandstone of the Franciscan Complex, specifically part of the Novato Quarry nappe. This is a thick slice of fine-grained sandstone that was laid down off the ancient coast of California, then shoved against the continent’s edge and pulled apart into lumps by the San Andreas fault system. A bunch of it underlies Marin County, and more makes up Point Richmond and El Cerrito as well as Piedmont and points south. This tectonic history probably accounts for the wear and tear visible in the roadcut.

When I visited the roadcut again last week, I annotated and recorded the site in the ROCKD smartphone app and announced it on Twitter. I’m trying out the app just for fun as a way to make some of my observations public. I’m looking at other apps for more rigorous mapping purposes.

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Geologizing on the 33 bus line

4 December 2017

My geologizing habits are unusual: being self-employed and semiretired, I go out on weekdays, when everyone else is busy and I have the landscape to myself. Moreover, most of my outings around Oakland are on foot, with the help of the Citymapper phone app and all manner of public transit, which I’ve praised before. In fact, I’ve written a whole compendium of places to see in Oakland this way.

So I’ve gotten to know the bus system pretty well. And for accessing lots of interesting, walkable terrain, the 33 line ranks right up there. Assembled from parts of the old 11 and 18 lines, the 33 runs from the bedrock hills and uplands of Piedmont, past Lake Merritt, to the bedrock hills and uplands of Montclair, taking in lobes 3 and 4 of the Fan as well.

The northern leg takes you to the well-appointed sidewalks of Piedmont, saving you a tedious climb. But there’s scenery on the way. First you pass the north arm of Lake Merritt, then cross lobe 3 of the Fan and reach bedrock right after crossing upper Grand Avenue.

Destinations in Piedmont include the former quarries of Dracena Park and Davie Tennis Stadium, the canyon and creek of Piedmont Park, and the headwaters of Trestle Glen Creek, plus smaller attractions like the slickensided roadcut of St. James Drive.

The southern leg of the 33 takes you to central Montclair, a jumping-off point for hikes in all directions. But first you pass the mouth of Lake Merritt, then enjoy a scenic ride up the valley of Park Avenue Creek and past the views over the glens (Trestle Glen and Dimond Canyon) in Glenview.

Above Glenview you could get off at Leimert Boulevard and trek through Oakmore, or go the other direction into easternmost Piedmont; your call. But then you’d miss the passage through Dimond Canyon.

From Montclair you can head west back downtown through Piedmont; north to Thornhill Canyon or past Lake Temescal to the Rockridge BART station; south to the trails of Joaquin Miller Park; or east to the high hills through Shepherd Canyon, up the Colton spine, and even all the way through Sibley Preserve, shown below, to Orinda.

None of those possibilities appear on AC Transit’s map of the 33 line, just a lot of human destinations and transit connections.

So climb aboard the 33 some time. Maybe I’ll see you there.

The Dunn-Spring Quarry, north Berkeley

27 November 2017

Glendale-La Loma Park, a little ballfield/playground complex in the north Berkeley hills on La Loma Road, is a repurposed quarry that’s had a true Berkeley history. The original quarry, operated by J. J. Dunn, appears to date from 1892. John J. Dunn, a Canadian immigrant born in 1839, was a major contractor in California building roads and sewers starting in the 1870s. This is Dunn portrayed in 1896 in the Oakland Tribune.

In 1900 Dunn advertised the quarry for sale “on account of sickness,” and died of Bright’s disease (kidney failure) in St. Helena that June.

In 1904 the Dunn quarry was reopened by Louis Titus, former head of People’s Water Company, as part of the Spring Construction Company. Its dawn-to-dusk blasting operations infuriated local residents, who obliged it to shut down in 1909 by threatening the business-friendly city council with a recall campaign. The company made the gaslighting claim that they were not operating a quarry, even though the rock from the pit was being used for streets and homes in the Thousand Oaks tract, but were in fact building a reservoir for the People’s Water Company.

After its abandonment the Spring quarry became an attractive nuisance, drawing generations of youngsters to its steep sides and deep swimming hole. Even those who didn’t swim in the cold, murky groundwater must have enjoyed the view.

In 1950 an 11-year-old boy drowned, and the city fenced off the quarry. The city acquired more property around the site in 1957, and eventually it became what you see today.

Unfortunately I have found no details of the site’s geology, although Titus called it a basalt quarry. The geologic map shows the downhill side as basalt of the Moraga Formation and the uphill side as the conglomeratic Orinda Formation.

This is the basalt. The brownish streaks are slickensides — friction marks from faulted fractures.

Other volcanic rocks here include rhyolitic tuff, a minor component of the Moraga Formation. It’s distinguished by its light color and broken (brecciated) texture.

Superficially, it resembles the Northbrae Rhyolite that makes up Grotto Rock Park and its sister parks, but unlike that heroically strong stuff it degrades quickly when exposed at the surface.

At the foot of the cliff you’ll find pieces of this excellent conglomerate from the Orinda Formation.

But the fact that it has crumbled down the cliff and will fall apart in your hands means that the rock face would be treacherous climbing. The city should be more forthright in discouraging climbing here; instead they just say “check out the other Berkeley parks with rock features…” Stay off it, and if an earthquake strikes while you’re standing there, jump back fast.

The Hillside School and the Hayward fault

20 November 2017

It was a most enjoyable hike that I led on Saturday for the Berkeley Path Wanderers Association, wandering for 3-plus miles in the city’s wonderful rock parks and along the Hayward fault. As usual, visiting the fault has its troubling side, and here I couldn’t ignore the implications of this splendid building, the old Hillside Elementary School on Le Roy Avenue.

This is the second Hillside School, built after the first one burned in the 1923 Berkeley Hills fire. For its time it was well designed, well made and well appointed, but after 50 years scientists confirmed that an active trace of the Hayward fault runs under it. The next major earthquake on this fault will rupture and ruin the structure. Besides that, the site is on a deep-seated active landslide.

The clear and present danger to children and teachers led the authorities to abandon the building in 1980.

In 2011 the German International School of Silicon Valley bought the site and pledged to do right by the building. In 2016 they fixed the roof with new, historically authentic materials, but at year’s end they moved out after deciding they couldn’t afford any more of the needed work.

There are two facts on the ground here. It’s a geological fact that this building is doomed and dangerous. But it’s an emotional and political fact that this building is precious.

The city declared the school a historic landmark in 1980, and it’s on the national register too. People love it and have strengthened the structure twice since 1925. But after the next major quake — not to mention a repeat of the 1923 fire — the school will be kindling, or ashes. Spending good money in a lost cause is an example of escalation of commitment, or the fallacy of sunk costs.

Without a building here, the site would be an excellent resource throughout the disaster period, and in between disasters an excellent little park.

During the walk, I made the modest proposal that we remove the building, and give it a nice funeral, before disaster strikes. Because now is the time that one day we’ll remember as “before.”

By holding a funeral for a building I mean, for starters, a respectful demolition. Make a virtual-reality model of the structure, recording the rooms and their beautiful wood beams and floors. Collect stories from the people who taught or attended school there. Hold a farewell concert in the old auditorium (with everyone signing waivers). Salvage the good materials. Build a memorial and have ceremonies.

All that stuff and more would befit the facts on the ground. I think it would raise the community’s consciousness of disaster preparedness, and at the same time mark the fact that in this case our ancestors won their bet against geology.