An early look at the Fan

4 September 2017

Lots of people love old photographs of familiar places, or old landmarks when they were new. I love old photos of Oakland because they show the land before it was paved over and/or forested.

The early California photographer Carleton Watkins was instrumental in saving Yosemite as a public park, simply because his large-scale images let people see its beauty and grandeur for themselves. But he also practiced his trade up and down the Pacific coast, including Oakland.

Here’s a stereograph he made here in 1876, looking east from the roof of the Grand Central Hotel at 12th and Webster. Click it to see its full 1000-pixel size.

Stereographs were made to be viewed through a simple apparatus that allows you to see a 3D image. You can do it without a viewer if you cross your eyes carefully. (Don’t worry if you can’t; you’re like most people.) To simplify things, I’ve turned one of the images into black and white and zoomed in a bit (800 px).

This is a pretty good image of Oakland’s high hills, the highest of which is Redwood Peak at the left edge. Lake Merritt sits between downtown and the hills of old Brooklyn. That hook in the shoreline is the cove where Wesley Avenue splits from Lakeshore Avenue today, heading left up a little valley. The right edge of the photo is where East 18th Street meets Lakeshore.

Between Redwood Peak and the shore of Lake Merritt, the top one-third is the high hills and the bottom third is the low hills. The middle third, hard to see, is the rocky hills above Piedmont and their eastern continuation in Oakmore and Redwood Heights.

Note that almost all of this is treeless. That was the state of the whole East Bay when the Spanish and the Americans came here. The exception was the redwood groves, which occupied the highest part of the ridgeline until they were logged out before 1860, and the coastal oak groves nearer the bay.

Anyway, what caught my eye in this photo was its view of the undeveloped lower hills that are almost totally hidden by houses today. Those hills were overridden first by wealthy estates, then by homes and apartments whose selling point was their views. To me, the real view was what those structures wiped out. Today only three bits of that terrain are left: San Antonio Park, Home of Peace Cemetery and Evergreen Cemetery.

Here’s how the Fan fits into that view. We’re looking east across lobe 4, the central segment of this ancient alluvial fan that dominates central Oakland.

Today, you can walk all over those hills and picture how they would have looked before development, but it’s a struggle. The old photographs are indispensible, and precious.

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A stroll up Indian Gulch, or Trestle Glen

28 August 2017

Once upon a time there was a thriving native encampment near the head of San Antonio Slough, tucked under bountiful oak trees in a valley with a permanent stream. Then the padres of New Spain put the natives behind walls to earn their bread with the sweat of their brows, and a generation later the Mexican rancheros converted them to secular laborers. The valley, which took on the name Indian Gulch after the Indians were gone, has remained significant. The property line between the lands of the Peralta sons, Antonio on the south and Vicente on the north, ran directly up its streambed.

On the map, the valley with its tributaries looks like a long feather, arcing across the bottom of this map from Lake Merritt (the former slough) into the hills of the Piedmont bedrock block.

Today the valley is an Eden of the suburban sort, well worth a walk for its natural and human sights. These sights do not include the stream, now called Trestle Glen Creek and mostly culverted or hidden in back yards.

The lowermost part of the valley, going up Trestle Glen Road, has a very gentle grade, taking well over a mile to climb 100 feet. The sides of the valley rise a good hundred feet on either side.

The stream here is at grade, meaning it has cut down about as far as it can. The ground it has eroded is the sediment of the Fan, not bedrock. See it here on the geologic map.

This stretch of the valley ends just past Norwood Street as we enter bedrock country.

The grade steepens slightly, and the valley walls close in a little. The power line towers in the back of this view sit on bedrock.

Two very unobtrusive footpaths lead from here to either side of the valley where you can encounter the bedrock. The one on the south side is particularly discreet; you might have better luck coming down from Park Boulevard via Elbert Street to see this exposure.

It’s your standard Franciscan metasandstone, the same stuff that was quarried in Piedmont before it incorporated in 1907. There’s also a nice exposure on Trestle Glen Road a little farther up.

By now the valley has gotten distinctly narrower and steeper. Right at the city line at tiny Valant Place, Trestle Glen Road leaves the streambed and climbs up to Park Boulevard. Seen from Valant Place, the valley is a real ravine now.

You can’t walk up the valley any farther; it’s all on private land. But from the Piedmont streets that flank the valley — Indian Road, La Salle Avenue, St. James Drive — you can catch glimpses of the living stream.

The Uptown to Montclair ramble I posted a few weeks ago goes through higher parts of Indian Gulch. But the longest stretch of the unspoiled stream, the western branch, is totally secluded in private hands. That branch is where the rancho boundary went. You can spot it from the 33 bus, on Hampton Street, if you know where to look.

So is this a glen, or is it a gulch? Both terms refer to small, steep-sided valleys with running streams in them. However, a glen is typically wooded — the word comes from the Gaelic — and implies a green, secluded place. A gulch not only has steep sides, but also a steep slope with a rushing mountain stream, and the word is widely used in the Southwest. A gulch is forbidding, but, especially in California, it’s well suited for gold panning. This valley offers both wealth and seclusion today, so I call it a toss-up.

Well water in use

21 August 2017

Once upon a time, we used to produce a lot of our water from local wells, but for the last century we’ve retired them as the aquifers were drawn down or polluted. So I’m always surprised and intrigued to see wells still at work. This is on Willams Street in San Leandro.

The location is a big educational complex comprising John Muir Middle School, San Leandro Adult School, and Woodrow Wilson Elementary. Presumably the well is for watering the grounds, not supplying the drinking fountains.

The water is a remnant of the once-productive San Leandro Cone, a body of sediment full of groundwater supplied by San Leandro Creek. The geologic map shows it as a set of fingers radiating from Lake Chabot, labeled “Qhl.”

Qhl stands for “Quaternary Holocene levees.” The Quaternary Period includes the last 2.6 million years of Earth history, and the Holocene Epoch is the final portion of the Quaternary, the time since the glaciers last melted. I think of the Holocene as the geological present.

Levees form when floods regularly spill over a riverbank — the moment rushing floodwater leaves the river, it slows down and immediately drops most of its sediment load. Repeat this enough times and a low rise builds up on both sides of the river: a pair of levees.

The map explanation says about Qhl, “these deposits are porous and permeable and provide conduits for transport of ground water. . . . Abandoned levee systems have also been mapped.” And that explains the well water of Williams Street — the street runs right down the middle of a former course of San Leandro Creek. Here’s a closeup.

The map shows that the Qhl unit coincides with an extremely gentle rise in the ground about 10 feet high and a quarter-mile across. Natural levees are rare to see, because humans build them up higher for “flood control,” but you’ll easily see the rise if you walk away from Williams Street a couple blocks and look back at it.

So San Leandro Creek once ran this way, must be thousands of years ago. Something perturbed it enough to cut a new streambed in another direction, and this abandoned course filled in. But it still carries water underground.

The northernmost finger of Qhl in the San Leandro Cone leads to the former site of Fitchburg, where a major wellfield once supported East Oakland with groundwater.

Coring

14 August 2017

With all the construction going on around town, you’ll see lots of drill rigs taking geotechnical cores. This one was at work at 2330 Webster, where the Webster Alexan development will go.

Just a few days earlier, a rig was collecting cores in the parking lot at 20th and Telegraph, slated to become one of two residential towers.

Crews like this are testing the ground to firm up the construction plans. The weight of these buildings requires a foundation that won’t sink, buckle or deform under the expected loads over the building’s life, including earthquake loads. At the Telegraph site two holes were bored, at opposite ends of the lot.

It takes a couple of workers to run the rig and a geologist to log the hole. They look the same — vests, boots, hardhats — except the geologist carries a clipboard and isn’t quite as muddy. The geologist on this job was a young guy, crouched in the sun and processing sediment plugs that looked like this.

It’s nice, clean marine clay from the lower part of the hole. I refrained from nibbling on a piece to gauge its silt content. It was real firm, not sticky. I’d put a house on it, no problem.

The geologist was poking at the plugs with a pocket tool and keeping them properly organized. He told me the hole was around 90 feet deep, with this stuff at the bottom. The top 20 feet was sand and gravel, then about 30 feet of clay, then some more sand and gravel and finally this clay. It’s a common pattern around the Bay, reflecting the changes in sea level over the last few hundred thousand years.

The crew was finished in less than a day, and they tidied up nicely afterward.

The U.S. Geological Survey’s Open-File Report 2014-1127, “Geologic Logs of Geotechnical Cores from the Subsurface Sacramento-San Joaquin Delta, California,” will give an idea of what core logging involves when it’s done right. What seems like painstaking drudgery is essential for building safely, and geologists can get called into court to vouch for the accuracy of their core logs.