Oakland geology ramble 4: Uptown to Montclair

24 July 2017

This five-mile urban hike is more of a terrain-and-streams ramble than a bedrock ramble. It climbs over 700 feet, winding through the watersheds that freshen Lake Merritt and traversing some of Piedmont’s wildest land. Although I’ve walked the route both ways, I’ll present it here from west to east.

The route goes from the 19th Street BART station to the heart of Montclair on La Salle Avenue, where every 20 minutes the 33 bus will take you straight back to the starting point. Or vice versa.

The terrain map shows the watersheds and drainage divides along the way.

This route is just one of several good possibilities. I have a thing about views, so I favor ridge roads that thread the divides between stream valleys. There are three streams here: Pleasant Valley/Bushy Dell Creeks (Grand Avenue), Wildwood Creek (Lakeshore Avenue), and Indian Gulch Creek (Trestle Glen Road). My route follows Warfield Ridge, the divide between the first two streams. The eastern alternative would go up Longridge Road, the divide between the last two streams. And, of course, one could take the low roads that follow the three streams instead. I leave those as exercises for the reader.

For completeness’ sake, here’s the geologic map. The blue areas are bedrock and the other colors represent various bodies of sediment.

The interaction of geology and terrain adds interest to the hike, but truth be told, the elegant and extravagant residences along the way are just as attractive as the geology.

On Broadway and Grand Avenue, you tread the level ground of the late Pleistocene marine terrace (Qmt) along the foot of the Fan (Qpaf), the large body of Pleistocene alluvium that’s one of Oakland’s most distinctive geomorphic features.

To the right of the Grand Lake Theater, the tall red-and-white building stands on Warfield Ridge. Behind it is Round Top. Cut to the right of the theater and make your way to, then up Warfield Avenue. That building houses the Grandview Apartments, and it’s well named.

Warfield, as I said, is a ridge road. It goes up and down a bit, but mostly up.

If you’re like me you’ll want to catch your breath every now and then. There are views on all sides. Pause and enjoy them. To the left is Pleasant Valley.

To the right is Wildwood Valley.

And behind is where you came.

Stay on Warfield all the way to its upper end, at split-level Wildwood Avenue. Go on up Wildwood. Right after you skirt Witter Field, in the valley of Bushy Dell Creek, you’ll enter the Wildwood Creek watershed for real, and also finally encounter bedrock.

It’s humble stuff, Franciscan sandstone. But it makes good crushed stone, and it supported several quarries before Piedmont took on its current identity. Take a closer look at the terrain here.

South of the blue line, you’ll see four small gulches eroded into this rocky hillside. The third one was a rock quarry that was later made into Oakland’s Davie Tennis Stadium. The others remained unexploited and are now thickly wooded. All four have running water still, thanks to our wet winter.

I picked the route that goes through the rocky headlands between these gulches. Turn right off Wildwood to Wildwood Gardens, and wend your way through this elegant neighborhood, across the top of the Wildwood Creek watershed, to the start of La Salle Avenue. Stay on La Salle all the way to Montclair.

La Salle crosses a fairly flat part of Piedmont, then leads along the rim of Indian Gulch, the village’s greenest and most secluded district. The road then goes up the floor of the stream’s middle branch. At its intersection with Hampton Road is a newly refurbished sports park where you can (and should) refill your water bottle. Higher up this little valley is a former reservoir named Tyson Lake. You can’t get to it.

La Salle becomes pretty steep here as you climb out of the valley and crest the highest ridge at about 725 feet elevation. The change in grade is the clearest signal that the bedrock is changing, according to the map, from Franciscan sandstone to Franciscan melange. But you can’t see that, either — there are no exposures of the melange along this road.

Instead you can see the high valley of Montclair, home of the Hayward fault, as you finally start down. A walkway painted on the road helps keep the locals’ cars back. In that respect Oakland is more walk-friendly than Piedmont.

And here’s the view back from the end of the line.

The Hayward fault is mapped right on the corner of La Salle and Moraga. You’ll see the offset curbs much better on Medau Place, though, one block north.

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The McKillop landslide: Ten years after

17 July 2017

In December 2006, I read a series of news stories about a landslide in Fruitvale, on McKillop Road, that took out a house and threatened two more, so I checked it out and was so impressed I wrote it up for About.com. This house was the victim.

And this was its front yard. When I revisited, last week, the three concrete steps were still there and the little pine tree next to them was over 20 feet tall.

This slump was the extension of an adjoining land failure earlier that year. In 2006 I was able to make my way across the top of that older slump and take this shot from the other side.

Nowadays the scene is well secured and overgrown with brush, but nevertheless the land is basically ruined. The city is storing some stuff there, and there are some beehives.

You can’t really fix landslide scars. On the human scale, they’re permanent. And landslides tend to feed on each other — when a portion of a slope fails, the adjoining slopes often follow. That’s the case on McKillop Road. William D. Wood Park is actually the scar of much larger landslides that have occurred, according to one report, since 1909.

The Oakland Tribune reported in 1936 after one such slide, “The property upon which the houses were built was originally filled-in ground from excavations made at the [Central Reservoir] site 15 years ago, neighbors said.” Throughout the 1940s and into the 1950s, it was routinely called the city’s worst landslide. Studies were made along with attempts to stabilize the slope, to little avail. Homeowners were putting their houses on jacks.

Everyone gave up fighting nature in the 1970s, and they made the land a park. And so far so good — here it was in 2006:

And how it looks today.

Nature may not have given up fighting us, though.

Peridotite-basalt lampposts

10 July 2017

The Lakeside Regency Plaza, 1555 Lakeside Drive, is the 15-story condo building next to the Scottish Rite Temple. Built in 1968, it’s definitely of its time yet of enduring taste. I paid it no mind until a few days ago, when I noticed the four artisanal lampposts that flank its driveway.

In their own way, these are even cooler than the serpentinite cladding I wrote about the other week. The large cobbles lining the shaft are peridotite, a stone that’s rare in the first place and not often usable in the second place. Peridotite (accent on the “rid”) is what the Earth’s upper mantle is made of. Because its minerals are more stable at depth than they are on the Earth’s surface, peridotite characteristically acquires an orange weathering rind as the iron content is released from its olivine and pyroxene crystals. It’s usually shot with veins of serpentine, which degrade its strength.

These cobbles are field stone, not quarried but gathered from the ground in their natural state. They probably came from a riverbed or talus slope in the Klamath Mountains.

The capstones, on the other hand, are lava — specifically, vesiculated (bubbly) basalt like that found in the volcanic Cascade Range. Lava is the opposite of peridotite, to put it briefly, the stuff of the Earth’s crust. These hand-dressed blocks may well have come from northernmost California too, in the vicinity of the Modoc Plateau.

Here’s a look at both rock types in closeup.

Or, of course, inspect the lampposts yourself next time you’re at the lake. I think of them as examples of deeply understated, perhaps even inadvertent, geologic wit.

HayWired, an imaginary earthquake coming in 2018

3 July 2017

Earthquakes are always a surprise, but we can be ready for them. Or, more ready. We can practice on a household basis, whether it’s a simple “Drop, Cover, Hold On” drill or a series of family meetings to go over scenarios — what if Mom’s stuck at work? What if we’re all out of town? What if we’re separated? What if our home is red-tagged?

It can be complicated. And think of how a whole city or region might practice for a major earthquake. The first requirement is a realistic picture of what would happen — a detailed, scientifically based earthquake scenario. When geologist Dale Cox first started talking to disaster responders about earthquakes, what they wanted to know most was “What exactly will the Big One be like?” He realized that his colleagues at the U.S. Geological Survey could supply realistic answers based on their research and “get the science used.”

Last week Cox told an audience at SPUR about a new scenario in the works for the Hayward fault, named HayWired. We’ll hear a lot about it on the Bay area’s unofficial Earthquake Day, April 18th, next year.

For scenario work, every region needs its own custom earthquake. Ten years ago, the first ShakeOut exercise in Southern California used a scenario quake measuring magnitude 7.8 that ruptured the San Andreas fault from the Salton Sea all the way to Lancaster.

For the Hayward fault — what Cox called “the most urbanized fault in the United States” — planners of the Hayward Fault Initiative have used a repeat of the magnitude 6.8 earthquake in 1868. They’ve also used a 7.0 quake that, unlike the 1868 event, would rupture the fault’s entire length. The new-and-improved HayWired scenario takes everything to a new level of detail and engagement.

Alameda County Courthouse before and after the 1868 Hayward fault earthquake. San Leandro Public Library (before) and Bancroft Library (after).

The HayWired scenario starts with a scientific description of the hazards connected to a hypothetical magnitude 7.05 earthquake that occurs on Wednesday, April 18, 2018 at 4:18 in the afternoon. It goes into far more detail than previous efforts, covering ground motions, landslides, liquefaction, fires, disruptions to communications and the digital economy (hence the “Wired” part of the name), and aftershocks and afterslip.

Aftershocks in the first two years after the HayWired earthquake. The largest aftershock, of magnitude 6.2, is a pretty major quake in itself. USGS image.

That description has been published as the first of three volumes. Other specialists are preparing two more volumes based on it, one on environmental and engineering impacts and the other on social and economic impacts. Those will come out in the next few months.

The HayWired earthquake originates in Oakland, 8 kilometers beneath the intersection of Skyline Boulevard and Joaquin Miller Road. For that and many other reasons, I’ll be following this project closely for you.