Oakland building stones: Lime stones

28 November 2016

There isn’t a good word for the full variety of carbonate building stones — limestone, dolomite, marble, marlstone and travertine. Although I like the word limerock, it apparently doesn’t really exist. In any case, these rocks aren’t very common in Oakland’s buildings, the way they are in, say, Washington DC (all of those memorials, and the Pentagon too).

Part of the reason is that limestone/marble is uncommon in California, and here it’s more valuable as an industrial material than as dimension stone. For limestone, think Indiana and Wisconsin. For marble, think Alabama, Texas and Colorado.

Panels of fossiliferous limestone decorate a building at 9th and Clay.

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Take a closer look at all the fossils.

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A builder might call this marble because it takes a polish, but in my language geologists call it marble only if the rock has been metamorphosed, and that would erase all of these fossils.

Its warm color indicates a certain content of clay minerals as well as calcium carbonate minerals (calcite or aragonite). If clay is present in amounts comparable to the carbonates, the stone is referred to as marl or marlstone. The Torrey Pines Bank building, on Webster Street, uses a striking combination of buff and black marlstone. A small building can pull off this look.

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The light stone is quarry-faced. The dark stone is fully dressed and then bush-hammer finished to lighten its color.

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This stuff has a few fossils in it, too.

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Limestone is a sedimentary rock that forms in warm, shallow seas where sea life, most of it microscopic, takes calcium carbonate out of solution to build its shells. These limy shells pile up and are consolidated into stone at low temperatures and gentle conditions.

You’ll see this environment in the Bahamas, for instance, but the current geological age is not a limestone-building time because the seas are so low. For most of geologic time the low parts of the continents have been warm, shallow seas. Hence the huge limestone beds of Indiana and the rest of the Midwest.

Then there’s travertine. It’s not marble in my language, but it takes a polish so it’s industrial marble. Here it is next door to the Torrey Pines Bank.

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A closeup shows its weird — I mean, attractive character, full of pore spaces and irregular layers.

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It seems like it might be fragile, but it’s very strong. The ancient Romans loved it, and Italy supplies most of the world today. The Getty Center down in L.A. is a veritable Disneyland of travertine.

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Mountain View Cemetery uses a lot of it too.

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Travertine grows in freshwater marshes, fed by springs of groundwater that’s full of dissolved limestone. It’s actually a renewable resource.

Marble, real marble, metamorphosed and recrystallized limestone, is a common accent and interior stone in Oakland. I like this balustrade in City Hall, which pleasingly contrasts detailed tilework against the warmth and translucency of fine marble. The stairs are marble too.

marble-cityhall

“What about dolomite?” you ask. “You mentioned dolomite up there.” The mineral dolomite, magnesium-calcium carbonate, can be present in limestone and marble without affecting the names we give those stones. Pure dolomite rock, or dolostone, is pretty unusual as a dimension stone. But Oakland has a spectacular example of dolomite aggregate used as the facing of the Kaiser Center, which I featured here a few months ago.

The Resilient Oakland Playbook

21 November 2016

Last month the city of Oakland released its long-awaited resilience plan, the Resilient Oakland Playbook. “Resilience” is the 21st-century name for the concept that communities can get up quickly when they’re knocked down, and avoid being knocked down in the first place.

I’ve always thought of resilience in terms of how we deal with natural hazards — earthquake, flood, landslides, sea-level rise, fire. Oakland used a definition that seems closer to familiar city politics and good-government ideas. Frankly, it read as if Mayor Schaaf had simply copied and pasted part of her recent speeches:

Resilience in Oakland means equitable access to quality education and jobs, housing security and community safety. It means building vibrant infrastructure to better prepare for shocks like earthquakes and stresses like climate change. In Oakland, resilience means catalyzing our diverse pool of talents and perspectives to tackle these challenges, both inside and outside our government, with particular focus on addressing the needs of the most vulnerable members of our community.

This will take some getting used to. The geologic hazard of earthquakes is given its due, although there are no new ideas in the playbook beyond the ongoing, snail’s-pace work of encouraging retrofits of old soft-story apartments. The Earthquake Engineering Research Institute, a major source of relevant knowledge that’s headquartered in Oakland, didn’t participate in writing the Playbook.

softstory

Emergency preparedness is represented by a seven-month “Love Your Block” initiative in the Fire Department’s valuable CORE program. That was supposed to start in October, but there’s no sign of it on the city’s website.

The geologic hazards of climate change (a possible rise in floods and wildfires) and sea-level rise are pervasive in the Playbook. That’s OK, although I consider them remote problems. They will slowly creep up on us, noticeable only if you take a snapshot every decade. We need to make long-term plans and float bond issues to deal with them.

But there’s no mention of the mud that wipes out roads in Oakland every year. A “vibrant infrastructure” has to deal with our chronic landslides.

thornhillslide

The word “landslide” isn’t in the playbook once — homebuilders in the hills, you’re free to continue business as usual. Houses on alluvial hillsides, you’re off the radar.

Oakland needs the things in the Resilience Playbook. But we need more than that — we need to cultivate what Robert Muir Wood, a writer I’ve long admired, calls a disaster culture. Last month in the L.A. Times, Wood pointed to the Dutch as exemplars, citing their centuries-long effort to win land from the sea. “What Holland created — a national narrative of resilience, shared by all the people — is what L.A. (and every city threatened by natural disaster) should aspire to. Today, with the power of information technology and education, it won’t take centuries to evolve.”

Disasters don’t wait decades, and neither can we. Maybe the Playbook is how we’ll get to resilience. I’ll be happy if it is.

A geologist’s reconnoiter of Piedmont

14 November 2016

The city of Piedmont sits surrounded by Oakland, like an organelle in a cell. I’m undecided on which organelle it might be — a mitochondrion (powerhouse)? a nucleus (brain)? Maybe just a vacuole of well-controlled living. Whatever the case, it’s a good walking town if you happen to be fit. And geologically it’s fully part of Oakland, occupying the best part of the Franciscan block. Lately I’ve been checking out the geology Piedmont has to offer. It varies.

The terrain is a rocky hillside dissected by small streams. Streets and homes tame this into an attractive rolling landscape.

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Once it was grassland, but today the land is heavily planted, and vistas are few.

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Although homeowners enjoy good views from their second floors, it is as if the public rights-of-way are deliberately shrouded, not at all like Oakland.

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But the hardscapes are robust and the plantings are gracious. Piedmont Park is the largest of the city’s public spaces and well worth exploring (here and here); so is Dracena Park. Don’t miss smaller features like the Hall Fernway.

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A little farther east is Crocker Park, where Oaklanders will find a familiar face.

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It’s a dark version of the statue “Bear and Cubs” by Beniamino Bufano that sits by the 10th Street entrance to the Oakland Museum of California.

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Whereas that one is cast in a concrete resembling granite, this is something else, an artificial stone of great character. The large polished clasts are a greenish black, probably serpentine (“black marble”), in a black cement matrix. It’s an understated tour de force.

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The official bike route through eastern Piedmont runs along St. James Drive, and there you’ll come upon bedrock at the head of Indian Gulch.

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The sandstone here is pretty sound, although no rock is immune to erosion. Occasional rockfalls expose the sandstone’s true golden color.

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The best exposure is around the powerline tower.

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Apparently someone there is who doesn’t love bare rock, who wants it green.