Lake Temescal, the west side

12 April 2021

For one of Oakland’s most rugged places, the west side of Lake Temescal doesn’t expose a lot of rock. But what’s there is unusual for Oakland, and interesting.

I’m talking about this ridge — tectonically, a shutter ridge — across the lake from the swimming beach.

The map of Lake Temescal Regional Park shows two trails there, the low one along the water and the high one up in the woods. An even higher trail, not marked on the map, is off limits and doesn’t expose much rock anyway.

I often wish I’d lived here in the 19th century when Oakland was new. It was in 1868 when Anthony Chabot acquired a steep little canyon back of the hills and built a dam to supply the young city with dependable water service. His technique, perfected in the gold fields of the Sierra, was to take a high-pressure water hose and wash down the sand and gravel from the hillsides to build the dam. I wish I could have inspected the scrubbed slopes at that time, but there were almost no trained geologists in the whole state, let alone me.

The canyon has a flat floor now, after decades of sedimentation, but you can see from the high trail that it’s still steep and narrow.

And the action didn’t end when Chabot finished the dam. He built a control tower in the new reservoir, but a landslide soon took it out. I’m guessing that was probably near the sluicegate where the beach house is today, and I’m guessing that the rainy winters of 1868-69 and 1869-70 plus afterslip and aftershocks of the big 1868 earthquake on the Hayward fault had something to do with it.

Speaking of which, two major strands of the Hayward fault run right through the reservoir. They’re helpfully shown on the map above. This is where the main strand crosses the dam. (Don’t worry, the massive dam will not fail even under the largest possible quake on this fault.)

The dam itself was raised and then lowered during the next few decades, and presumably the lake rose and fell too. Meanwhile trees and brush moved in upon the slopes where the Ohlone had previously maintained grassy meadows, and the rocks decayed and soil built up.

And the rocks themselves embody the complicated history of starting out in a vigorous subduction zone, being deeply buried and exhumed probably more than once, then being torn up and shoved around by the San Andreas fault system of which the Hayward fault is part.

All that is to say that Lake Temescal is a dynamic area at all time scales. It’s more complex than the small-scale geologic maps can show, even though it’s complex enough on that map.


KJfm, Franciscan melange; ch, chert block; af, artificial fill; sc, silica-carbonate rock; sp, serpentinite; Jsv, Leona volcanics; fs, Franciscan sandstone; KJkm, Knoxville Formation

The west side is mapped as melange, which is basically a mess of mashed-up sandstone with big blocks of other rocks, each with its own separate history, suspended in it. The little blip labeled “ch” is this block of chert at the top of Hill Road. So when I visited the west side trails last week, I expected to find things I didn’t expect. And most of the rock along the trails appears to be nondescript sandstone — I say appears because since hammering is forbidden, it’s hard to find a fresh surface. But lo and behold, along the high path coming down from Broadway Terrace, there’s the telltale gleam of blueschist in the exposed subsoil.

The color really comes out when you wet a piece.

Other apparently high-grade metamorphic rocks include this hard, glittering schist. Not having access to thin sections and petrographic microscopes, I can’t check for the presence of jadeite, which has been reported in blocks from this melange.

And over at the north end of the train is a distinctive outcrop of another schist. Hard rock supports slow-growing lichens, and the species differ depending on the rock’s chemistry.

Underneath the lichens, the rock is a bluish-gray mixture with a strongly folded texture, both signs of a rock that’s been through a lot of distortion at high pressure and temperature. These photos are from exposures by the lawn. The first shows the folding and the second shows fault-related crushing on the left side. The crushed material is called gouge, and bits of it are common in this sector.

My authority on Oakland’s Franciscan rocks, John Wakabayashi, holds that the west side of the lake hides the same ancient major thrust fault — a megathrust, in fact — that’s famously exposed in El Cerrito above the recycling center, where high-grade rocks have been pushed above lower-grade rocks. Unfortunately the fault itself appears to be in “a brush-filled gully with no exposure,” so it may be a while before we ever learn more.

But I did learn something more last week, about the beach house.

It is made with the local rock, namely the Leona volcanics. Whether the stones came from the hill just upslope to the east, the one that collapsed in the 1870s landslide, or from across the freeway in the great Tunnel Road cut during the 1930s, I do not know. I’m guessing the former, but I would be happy to be wrong if it means I can be certain. Putting the building and the roadcut in the same photo, there is a resemblance.

The fun thing is, both locations can be closely inspected. That sounds like a good afternoon project.

Posted in Franciscan rocks, Leona volcanics, Oakland blueschist, The Hayward fault | 1 Comment »

Rock garden coming to Lake Merritt

29 March 2021

The Gardens at Lake Merritt are building a rock garden in the heart of the grounds. They have plenty of gardens with stones in them already, but this will be a proper rockery. This post is about the work in progress. I know almost nothing about the plants they’ll be featuring, but I do know a little about rocks.

As we enter yet another year of drought, it’s important to note that rock gardens are made to conserve water. The stones and gravel offer solid shade to the underlying soil, and the typical plantings are small, hardy species from alpine or desert settings. As you bend down to admire these plants, have a look at the stones.

The location is between the community plots and the Torii gate, the crossroads of our remarkable garden complex. Just across the path is the hill-and-pond garden, where the turtles hang out.

This view toward the lake shows the layout. In the background is the entry to the Sensory Garden, which has had a thorough going-over during the shutdown.

The foreground containers in both photos showcase rounded river stones, blue-green argillite most likely from the northern Coast Range. I would not be surprised if some of the rock nuts of the Suiseki Societies of Northern California contributed to this project.

The center of the garden is a mound of sandstone tablets, with some accent stones, oriented north-south for optimal sun. Rings of different colored gravel surround it. Note the “do not climb” sign.

Some of the basins echo the brown sandstone of the central mound, offering textural contrast.

Others contrast more strongly. Here rough greenstone is set in crushed marble.

And what would a Northern California rock garden be without some red chert?

All of these rock types are typical of the Franciscan Complex, a lithological scrapple that makes up the bulk of the northern Coast Range, including San Francisco and the hill that Piedmont sits on. Get to know them, and you’ll see them all over the place.

The Gardens at Lake Merritt have several sectors that artfully mix plants and stones. The water garden I mentioned earlier is one, and there’s the cactus garden and the bonsai garden (which has just added a suiseki section) and the enclosed Japanese garden by the Community Center building. They’re all looking great right now, but check the hours before you go; weekends are still closed.

A few years back I wrote about the remarkable rock garden assembled by Ruth Asawa in San Francisco. As the world reopens, I hope to visit it again.

Posted in Franciscan rocks, Oakland stone | 1 Comment »

Geology’s problem heritage

15 March 2021

Part of being a passionate student of geology is coming to terms with its history. The easy part for me is imagining those good old days, when pioneering curiosity-driven people looked around with fresh ideas and fresh eyes, rock hammers in their belts, and made lasting names for themselves. What a pleasure it would have been in centuries past to hang with Hutton in the Scottish countryside, to dig fossils in the Paris Basin with Cuvier or minerals in Italy with Dolomieu, to tramp the Alps with Agassiz or the Andes with Humboldt, or to join in the learned debates of the 19th-century British scientific societies.

Then there’s another part of geology’s history that it shares with so much else in science: the dominance of white men and their self-serving causes. I’m old enough, and have seen and read enough, to have gotten a sense of American geology’s good old days and how their influences linger. I’m free to imagine myself being with those great men of geology as a fellow educated white guy, born in the club.

The good old days were an intimate part of the Westward Expansion, which began for geologists with the 1825 gold rush in North Carolina and ended with the Alaska Pipeline in the 1970s. The eastern states funded the first “geological surveys” in the 1830s, state-supported projects to help develop the state’s natural resources. The object was to suss out the territory: to find and map promising mineral deposits so the state could license or sell them to help bring about new wealth. The federal government did the same in the western territories.

This high-minded purpose existed within a political setting of colonialism and imperialism. It relied on official and unofficial theft of Indian lands and genocidal policies against the tribes, carried out with American efficiency and enthusiasm. It relied on the support of the slave states seeking fresh land for their cruel system and the free states, opposed yet conflicted. It relied on the railroads and the power they exerted on behalf of the markets they served. It relied on taking land from other nations as war prizes. The benefits accrued to the white men in command.

The heirs of these men, raised on generations of selective history, may have forgotten their forebears’ cruelty and aren’t inclined to admit its aftereffects, but you see them if you just look around.

In classrooms and textbooks, the saga of science that threads those times is scrubbed of this context. John Wesley Powell is the hero who traversed the Grand Canyon and mapped its rocks, not the ethnographer who disparaged the people along the way that he studied like beetles. Clarence King is the hero “of good English stock planted on New England soil” who mapped the high Sierra and launched the U.S. Geological Survey, not the twisted soul who deceived his common-law wife, a Black woman named Ada Copeland, until confessing on his deathbed.

Last week I found something that helped me cut through more of the unthinking nostalgia that veils our scientific history in a golden haze. It’s a set of PowerPoint slides called GeoContext, easy to drop into a presentation, that treat a few selected topics in the history of geology. Powell and his generation are there, in the deck on “Landscape and Scientific Racism.” The object is to add context to the standard history to make it plain that, among other things, American geology arose as the servant of an expansionist, racist society. And that history, the site’s creators argue in an interview, is an underlying reason why people of color and women keep having to fight headwinds in their geoscience education and careers.

We have examples of the checkered past in Oakland, like Joseph Le Conte, the scientific racist who taught geology at UC Berkeley. More generally, Oakland was founded on the crime of land theft from a family who was granted the land as a reward for kidnapping the Indians who lived on it. Everything stems from that. But to illustrate the tenor of old times I think of Oakland’s rock quarries.

This is Dracena Park. On this site, in the early 1850s, Walter Blair established a quarry that supplied much of the needs of the growing city for crushed rock. He hired Chinese workers, who being at the bottom of the social ladder were the cheapest labor around. But growing anti-Chinese sentiment and outright legal bans drove them into crowded “Chinatowns” or out of the state entirely. Blair gave up the headache (he had lots of other business interests) and sold the pit. The successors worked it for a few more years and then abandoned it, leaving a “swimming hole” in which several children drowned over the next few decades. It took a hundred years before the site was turned into a park. Blair owned this land and felt free to leave a mess behind. That’s the kind of capitalism California is built on.

Competing rock quarries stayed alive with white laborers. The two largest, Oakland Paving Company and Alameda Macadamizing Company, hired Italian and Irish immigrants, respectively. In the late 1800s they split the city between them in a well-known duopoly — in its part of town, one would underbid the other by half a cent per yard — that kept their workers low-paid and kept rivals from growing. Both firms left behind large pits that festered for decades before being repurposed, one as a shopping center and the other as a tennis stadium.

Like the song goes, don’t look away, look around. Our history doesn’t make us bad people, but it does bring us up against things we’re responsible for fixing.

Posted in Other topics | 3 Comments »

A pause in the disaster

1 March 2021

Early on in the Covid-19 pandemic, it occurred to me that the nationwide disease outbreak was exactly like what most of us call “natural disasters” — floods, droughts, heat waves, wildfires, hurricanes, landslides, earthquakes of course, and the like. And in the literature, and on Twitter, I started to pay more attention to the specialists. Not so much the specialists in the phenomena, although those are crucial people, but the specialists who call themselves part of the disaster community: social scientists rather than natural scientists.

Those are the people who hate the term “natural disaster.” They’ll tell you “there are no natural disasters.” By that they mean an insight that galvanized me when I first read it a generation ago: “Human beings, not nature, are the cause of disaster losses. The choices that are made about where and how human development will proceed actually determine the losses that will be suffered in future disasters.”

It underlies what I do in this blog. It was in this book.

Disasters by Design came out in 1999, the outcome of a conference of disaster-related specialists sponsored by the National Science Foundation and several federal agencies. It laid out an ambitious vision of how society can deal with the disasters that happen when we get in nature’s way.

First, it pointed out that our current practices of mitigation aren’t enough. Our warning systems, building codes, and other measures succeed only in saving lives. Consider the case of hurricanes: they no longer kill many people, but they still cause record-breaking economic losses every year. Even the small ones cost more these days. Hurricanes haven’t changed much at all, but we have. The Northridge earthquake of January 1994, not such a big one, killed only a few dozen people, yet it caused more than $20 billion in insured damages alone.

And our mitigation measures have bad side effects. For example, the hurricane warning system makes people feel safer, but now it’s harder to keep them from building on the beach, from paving the dunes, from moving sand from one coast to another for short-lived patches on degrading shorelines. And in earthquake country, new structures preserve people’s lives, but the growing population is still vulnerable, living too far from jobs and served by elaborate electrical and water systems. People die less and less, but they keep paying more and more. Surely we can do better.

Disasters by Design explores how to go beyond mitigation toward a more resilient way of life, one that rolls with nature’s punches and returns to normalcy quickly. This desirable goal, “sustainable hazard mitigation,” means living politically the way we live personally, in ways our descendants won’t end up paying for. And if it’s done right, the community gains benefits beyond the insurance that the new policies provide — the people and their institutions are stronger, and wealthier too. That great work needs the help of social scientists, whose research on the people side complements the expertise on the engineering and prediction side.

The reason this book was a best-seller for its publisher, used as a textbook for a generation of practitioners and launching a movement in and beyond the disaster community, was its author. Social scientist Dennis Mileti was a gifted communicator who could hold an audience without a PowerPoint deck, a teacher who always had time for a student, and a leader who knew how to energize and drive diverse committees and teams. He went to the same conferences I do, and I sought out his talks.

Mileti died of Covid-19 on 30 January, two days before he was scheduled to get the vaccine. Last year he told a writer for the Washington Post that America’s approach to the pandemic scared him: “We have people saying, ‘It will be over soon!’ and other people saying, ‘It could be months.’ That gives the public the ability to pick the answer they like, which is the No. 1 no-no in public messaging.”

I opened my copy of his book last week — and it’s his despite having dozens of contributors — and it does not read like it’s 21 years old. The vision is still strong and the insights are still valid. You might say that means we haven’t achieved sustainable hazard mitigation, and in truth that’s a very difficult project. It takes everyone’s involvement, under skilled and patient guidance, to change a community.

But for some reason being reminded of the vision is still inspiring. And over the years I’ve seen the vision infiltrating my own piece of the disaster community, the Earth hazards sector. Tsunami specialist Lori Dengler wrote an appreciation of Mileti just last fall, which reminded me that he was involved with the ShakeOut earthquake-drill program, and before that was an advisor for this pamphlet many of you may remember from after the Loma Prieta earthquake. Dennis Mileti worked here too, for us.

And that’s just the earthquake crowd. He was involved with the full range of disasters, bringing insight into how to communicate alarms and alerts, what motivates genuine change, what steps to take beyond reciting facts at people. And yet it was a funny thing: while Mileti died of Covid-19, Disasters by Design doesn’t address disease epidemics. But over the last year I’ve read a lot of pandemic coverage, and awareness is seeping in that disease outbreaks are just part of this planet, and that if we are creating situations where animal viruses can leap to our species — imperiling ourselves by getting in nature’s way — then Covid-19 is just as much a “natural disaster” as a levee break during a flood.

It may be time for a new book that adds pandemics to the rogues gallery of disasters. It would be fitting if we could tie together the lessons learned from the pandemic and the quest to bring about sustainable hazard mitigation. Sustainability is about not just growing wisdom, but also passing wisdom forward, and Dennis Mileti did both. Let us not forget his name.

Posted in Oakland hazards, Other topics | 1 Comment »

« Older Entries
Newer Entries »