The litter spectrum, benign to unholy

14 May 2018

The litter on the land falls along a spectrum. This disembodied deer hoof does not qualify as litter because, as far as I know, a human didn’t leave it on this abandoned, overgrown fire road. I felt no obligation to do anything more than pause and contemplate it.

At the opposite end of the spectrum is this spectacle just off Pinehurst Road on well-posted watershed land. I felt ashamed on behalf of humanity, but could do no more than pause and contemplate it.

Fortunately, that same day East Bay MUD had a crew nearby with a backhoe and related equipment, cleaning up an even worse litter pile.

That leaves a wide space between the two ends of the spectrum with different judgments to make and responses to consider. This next photo of cannabis seedlings is a few years old, and maybe these days people are doing a little less surreptitious planting in our out-of-the-way places.

It’s possible to do this without making an unholy mess, but I’ve come upon several instances in Oakland’s hills and they were all unholy messes of degraded plastic, bags of spilled fertilizer and remnants of crude camping practices. And the plants didn’t look very good either. So these seedlings . . . I left alone with a sense of foreboding similar to what I’d feel upon seeing fresh bear scat.

Stuff like this dead mylar balloon, lost from some celebration and fallen to ground way off the trail in upper Grass Valley, makes me feel ashamed . . .

but I’ve learned to stop stewing and just pick it up. One by-product of my quest to reduce my collection of rocks (I no longer call it a rock collection) is a growing set of used baggies. I pack several and fill at least one each outing.

Turns out that while I’m not that much of a hiker — just a flâneur of the hills — I’m right up there with the hardcore wilderness walkers who carry trash bags as their eleventh essential. It’s a practice I urgently recommend you follow too. Maybe we can’t fix the unholy messes that way, but it beats shame.

And here and there, you come upon trash that is picturesque.

And occasionally you come upon a thoughtful act of self-expression, around some corner where it’s been waiting to meet you. That’s what my next post will be about.

In other news, I’ll be leading a walk for Oakland Urban Paths next month visiting some of our historic former rock quarries. That’s in addition to the Oakland Heritage Alliance walk I’m leading in July. Also in the works, a walk for the Friends of Sausal Creek.

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How useful is the Orinda Formation?

30 April 2018

Walking along the paved trail north of Inspiration Point, I was brought up short by a splendid outcrop of conglomerate.

It’s strongly reminiscent of the Orinda Formation conglomerate exposed to the south in Claremont Canyon, in Sibley Volcanic Preserve and along Route 24 east of the Caldecott Tunnel.

Naturally I fired up the geologic map (I keep USGS map MF-2342 on my tablet) to see how the locality is mapped. It’s the little hill northwest of Inspiration Point, right above the word “Nimitz” where a power line runs.

But instead of Orinda Formation (the orange unit labeled “Tor”), which underlies Inspiration Point, it’s mapped as “Tus,” or “unnamed sedimentary and volcanic rocks (late Miocene).” Turns out there’s a major fault that separates two big blocks of young East Bay rocks — that thick black line with the teeth that represent the upthrown side — and even though the rocks look the same, we can’t say for sure they are.

The area of “Tus” rocks is rather large; in fact it’s the largest single rock unit on the geologic map.

I poked around the literature and found that the Orinda Formation has drastically shrunk over the years. As one example, here’s part of a 1973 map of the Lafayette area (Calif. Div. Mines & Geology Map Sheet 16) that classified a bunch of rock as Orinda Formation, drawn with the exquisite attention that emanates authority.

But the details are quicksand. First, the map is not about bedrock per se, but landslide hazards. Second, the author’s citations are generally very old, not that there’s anything wrong with that, but still. Third, the author’s idea of the Orinda is a unit that mixes lava beds (lumped today in the Moraga Formation) with the coarse sediment that defines the Orinda today. A long footnote explaining his thinking shows that he basically made an arbitrary choice of stratigraphic nomenclature to match the informal usage of local engineering geologists, who tend to talk about “Orinda-type” materials (like I was thinking at my outcrop) without making sure the stuff actually matches all the criteria for the Orinda Formation.

I’ve read my share of geologic engineering reports; any large construction project has to have one prepared. They’re good for their purpose — ensuring that the work is suited for the ground — but they don’t critically assess all the details of the science. And they probably shouldn’t. Instead, they line up the existing literature, outmoded and current alike, and discuss or dismiss it on the way to reaching their conclusions and advising their client.

Maps like Sheet 16 propagate obsolete or informal nomenclature, and thus stratigraphic concepts that are outmoded or discredited persist in the geotechnical literature like zombies long after research scientists have moved on. But I don’t blame people. The old idea of the Orinda Formation, widespread and simple, was very handy. The current idea of the Orinda, constricted and specific, is less handy because it leaves a large area of bedrock with the mumbly label “unnamed sedimentary and volcanic rocks (late Miocene).”

Geologic maps aren’t written in stone. Only stone is, and we’re still learning to read it.

News from the HayWired fault

16 April 2018


The ruins of Morse & Heslop’s mill, Haywards, after the 1868 earthquake (Bancroft Library image)

This week the media will mark San Francisco Earthquake Day, 18 April, as they always do but with an extra message for 2018 — this year will be the 150th anniversary of the original “Big One” in the Bay area, the Hayward earthquake of 21 October 1868. The U.S. Geological Survey and a host of partner agencies and organizations will roll out the next piece of a master plan that will guide the response to future large East Bay earthquake on our very own Hayward fault, usually called “a ticking seismic time bomb” by the intrepid researchers who get in front of cameras and audiences.

That first piece, Volume 1 of a planned series, is a scenario called HayWired: a description of a typical magnitude-7 earthquake, modeled after the 1868 quake, presented in as complete detail as we know how, with a special focus on its probable effects today in our highly electronic state. It’s online now at the USGS site.

I wrote about this project here last July, so you can read that post for more background. After that you may enjoy the USGS’s “geonarrative” about HayWired. It’s awesome, but only on a touchscreen device.

Today, though, I wanted to provide some details from the original quake. In 1868 a committee was convened to create a report on the event, but it never finished a report, so whatever work they did was lost. We only know as much as we do because after the San Francisco earthquake of 1906, the commission set up under UC Berkeley’s Andrew Lawson to investigate it decided to add a chapter on previous earthquakes. There were enough survivors of 1868 at the time to record quite a bit of detail. So here are some tidbits from the famous Lawson Report of 1908 about the Hayward quake of 1868.

The great shock happened about 7:50 a.m. on 21 October 1868, and ground ruptures were recorded, with 3 feet of offset in some places, from Mills College down to Warm Springs. North of San Leandro, though, “The county was then unsettled, and the information consisted of reports of cow-boys riding the range.” From Oakland we have these details:

  • “A house near old Blair Park, in the present Piedmont district of Oakland, was badly damaged.”
  • “Pans of milk and tubs of water emptied out almost in a moment, trees whipt about like straws; many houses twisted 5 or 6 inches out of square, particularly those on brick foundations.”
  • “In Brooklyn, as in Oakland, many chimneys were broken off at the roofs.”
  • “The bed of San Leandro Creek, which had been dry for several months, became filled with a stream of water 6 feet wide and a foot deep.”

At Haywards (the name of Hayward at the time) and neighboring towns, “nearly every house was thrown off its foundations.” Dozens of aftershocks were recorded in Haywards during the first 12 hours.

R.C. Vose of Roberts’ Landing wrote, “Our house broke in three pieces, each part falling outward. A boiler of hot water was on the stove, and with the first deafening jolt, the hot water came my way, giving me a bath I have never forgotten.”

In Fremont, Tyson’s Lagoon, the body of water next to the BART station, drained dry and remained dry for three years.

In San Jose, situated as it is in a large sedimentary basin, damage to brick buildings was universal.

12 aftershocks felt in San Francisco during the first day. Damage was most severe in the “made land” (artificial fill) in the former Yerba Buena Cove. Out at the Cliff House “the shock, however, did no damage, not even upsetting the glassware in the bar.” Ships at sea felt strong vibrations, like running aground or the anchor chains running out.

The earthquake was felt in Chico and many Sierra foothill towns, even in Carson, Nevada. Damaging shocks were reported throughout Sonoma County, as well as in Stockton and Sacramento.

All of this will happen again the next time a major quake strikes the Hayward fault. However, today there are hundreds of times as many people living in the affected areas. Back then, about 30 people died. Do the math and pay attention this week.

Land and rocks of westernmost Piedmont

2 April 2018

The western end of Piedmont includes the headwaters of Pleasant Valley Creek, which is tucked under Grand Avenue. But the slopes and gullies of the valley can’t be hidden, and what may seem like a scramble of streets is a nice place to walk around. The topography I’m talking about is north of Oakland Avenue, between Grand and the former quarry of Dracena Park.

None of it’s bedrock; nothing wrong with that. It’s the uppermost part of lobe 3 of the Fan, that big arc of ancient alluvium hills across central Oakland. The bedrock part, farther uphill, is much steeper walking, and the rock (the blue field labeled “Kfn” on the geologic map) doesn’t show itself either.

I should make an exception to that statement — Dracena Park is a great place to see the bedrock. But for the purposes of this post it’s just a pretty place, either in the former main pit:

or in the valley on the north side, now full of redwoods.

This is the most dramatic bit of stream valley in the area. Elsewhere, it’s easy to trace the drainage lines; in fact during our recent batch of rain, you could see water coming out of the ground just like in the old days before people lived up here.

This slopy bit of suburbia is criss-crossed with hidden history. The Key System streetcars used to serve the neighborhood. Indeed, a railroad syndicate once planned a major route through here that was going to run through upper Fruitvale and on to San Jose. The right-of-way appears in this 1927 map (courtesy of the Oakland Library History Room), long after the plans were abandoned.

The part of it running as far as Oakland Avenue did end up with rails as part of the Key System’s C line. If you look closely at the area in Google Maps, the lot lines give the route away.

The transit routes, road and rail, took advantage of the saddle in the ridge of lobe 3, at this spot where Pleasant Valley Road eases over the hill and becomes Grand Avenue. The view is west across the saddle toward Rose Street.

OK, enough of that. There are indeed rocks in this neighborhood. See that clever stone wall in the foreground in the previous shot? Here’s a closeup.

Other rocks are more laid back, understated but cool.

Still others, the only word for them is homey.

They’re all mostly landscapers’ stone, purchased at a commercial yard. But here and there you’ll see genuine domestic Oakland rocks. This little wall is made of serpentine/blueschist from around here, probably the pit at Serpentine Prairie or nearby.

And the Franciscan red chert is very likely from Piedmont itself, which sits on a hill of melange, a marble-cake rock unit that mixes chert, basalt, sandstone and serpentine in a mudstone matrix.

Some of it can be downright psychedelic. Stuff like this was quarried in Piedmont before any buildings were here at all.

Even the sidewalks, the oldest ones anyway, incorporated aggregate from Piedmont’s original quarries.

The town has grown up since then. It puts on a good front — very nice homes, lovely grounds, a fine place for walking and taking in the views (especially when the leaves are down in winter). But it began as a rugged, dusty mining district with horses and dynamite.