Walavista valley, 1916/1925

I have found a new time sink at the Online Archive of California, where this photo of undeveloped Walavista Avenue, from 1916, is posted as part of this collection.

The camera is on top of Warfield ridge, west of Lakeshore, just uphill from Fairbanks Avenue. The wooded gulch at back left is the charming little valley that Portal Avenue runs up, right at the Piedmont line. The Alameda Quarry, where Davies Tennis Stadium now sits, was just to its left, discreetly out of this developer’s portfolio photo.

Here’s roughly the same view in 1925. The view from there is still nice, but much more obstructed today.

The street on the left is Arimo Avenue, running up the smallest of the ridges south of Lakeshore, and the ridge on the right is populated today by Balfour and Calmar avenues. It is fascinating to see this topography in its original form.

Tunnel approach

I’ll be taking a tour of the new Caldecott Tunnel bore on Friday. This is the view of Route 24 from the ridge south of it, across from Hiller Highlands. Everything here is east of the Hayward fault.

On the right is uppermost Broadway, where a line of locals and advanced commuters chronically hope for a few seconds’ advantage by merging at the last second before the tunnel. I’ve decided that it’s faster to get in the left lane of 24 as soon as possible and stay there. Anyway, all the land from here to the far curve is underlain by rocks of the Great Valley Complex, of Late Cretaceous age. A fault separates it from the Sobrante Formation behind it, which is much younger. The lower part of the skyline ridge is Sobrante, but the high part is chert of the Claremont Shale. The tunnel penetrates both of those units, and I hope for a good look at it.

I was standing by the power line; you get to it by hiking down the road from the sports complex, on Broadway at the overcrossing, or by ducking around the gate at the top of Pali Court. The Great Valley here is a mix of fine-grained sedimentary rocks. Exposures are poor and the fabric is disrupted. Here’s an exposure on Pali Court.

And here’s a closeup from nearby.

It’s very shaly. The lenses of more siliceous stuff don’t add to its strength.

Fault valley

October 21, not October 17, is Oakland’s real Earthquake Day. While many of us remember the 17th vividly, the day of the Loma Prieta quake in 1989, the morning of October 21, 1868 was when the original Great San Francisco Earthquake struck. It was on this side of the bay, on our own earthquake fault, and the ground cracked from Fremont all the way to the edge of this view from the end of Pali Court, in the neighborhood just across route 24 from Lake Temescal.

The Hayward fault runs from the notch on the skyline, which is in Montclair, to the right edge behind the house in the middle distance. This part of the fault, between Mills College and Lake Temescal, is the only place that has large areas of bedrock on both sides. What that means for the purposes of today’s post is that it’s the most rugged and picturesque part of the fault and has probably the greatest concentration of million-dollar homes.

Today I invite you to review this blog’s category “the hayward fault.” I seem to have rattled on at great length on this subject. Some day the fault will rattle all of us at great length.

Today’s Oakland Tribune has an article about newly mapped faults in the Hayward fault zone; I won’t link to it because the Trib’s links die quickly. But the new Alquist-Priolo zone map can be accessed here.

Calmar, Mandana, Longridge

I’ve been exploring the surprisingly intricate topography between Lakeshore Avenue and Park Boulevard, where I count four separate ridges separated by three valleys. From the ground, it’s a challenge to visualize and photograph. This is the view across Mandana valley from the side of Calmar ridge, on Santa Ray Avenue, to Longridge.

I haven’t forgotten the blog, I’m just real busy. The weather lately has been superb for walking.

Linear scarps

Next Saturday, 8 September, I’ll be leading a short, rugged urban walk for Oakland Urban Paths that among other things will visit these faceted spurs along the Hayward fault. Seen from the north . . .

and from the south:

The downhill side is moving north with respect to the near side. The open land in the foreground is the King Estates Open Space.

This will not be a stairway walk. The off-street passages are steep, weedy dirt paths that have not been maintained. The land along the fault is steep, making for nice residential view lots. I haven’t finished the route yet but it will take no more than 90 minutes, 10 to 11:30—I have a lunch destination I’m anxious to make. So I would like to set a good geologist’s pace. Details and questions as they come to you over at Oakland Urban Paths.

Lower Piedmont Park walk (#28)

Walk number 28 in Charles Fleming’s Secret Stairs East Bay winds around the fine homes and hills of Piedmont along the valleys of Wildwood and Bushy Dell creeks. Here’s the route, shown on the Google Maps topo base.

The first and last part of the loop is in the watershed of Wildwood Creek while the rest is in the Bushy Dell Creek watershed. (They run down Lakeshore and Grand Avenues respectively, separated by Warfield ridge, and combine down at Lake Merritt where their names are sunk in bronze by the pergola.) Geologically, the walk covers the uppermost part of the big Pleistocene alluvial fan and the edge of the Franciscan bedrock block that underlies most of Piedmont.

We start at the Lakeshore-Winsor split in the stream valley and make our way toward the divide. On Portsmouth Road the high ground of the bedrock zone stands out ahead.

At the far end is a steep climb to Wildwood Avenue, where we can look back across the stream valley to the ridge topped by Calmar Avenue, on the Oakland side of the city line.

Turning the other way, we look over the valley of Bushy Dell Creek. Once a large formal garden, this part of the valley was filled and leveled for its current use as a sports complex. It appears never to have been a quarry, unlike Dracena Park to the north or Davie Tennis Stadium to the south.

We turn upstream along the creek, where the land is relatively untouched. Just above this spot is the site of what was reputed as a sulfur spring.

The geologic setting doesn’t really give much support for the presence of a proper sulfur spring like the one in Walnut Creek, but after all this time the question is moot. Certainly I didn’t notice any odor. The grotto was very pleasant anyway, and there’s real bedrock all around. It’s mapped as Franciscan sandstone of the Novato Quarry terrane.

The route goes farther up and takes a loop past a pair of boulders.

Take a close look at these: they’re genuine Oakland-style blueschist, globs of old ocean crust that have been carried tens of kilometers down into the earth along a subduction zone, then spat back out, possibly more than once. (The details are at the bleeding edge of California geology.) The one boulder displays good color and mineralogy:

The other has some nice slickensides to show us.

Coming back downstream and past the baseball diamond, we pass the entrance to the football field. The view looks down the valley toward the lake and downtown.

Near here we can see more exposures of the sandstone bedrock, but soon afterward the route returns to the alluvial fan. The two substrates make subtly different topography, but that can be hard to see given the heavily landscaped landscape.

Palm Drive offers a picturesque farewell view of the Bushy Dell Creek valley.

Again we cross the divide between the two watersheds at Wildwood Avenue. The near valley is accentuated by glimpses of the higher hills.

I never get tired of this stuff.

Here’s the route in more detail.

Bella Vista hill

Bella Vista hill is part of the big Pleistocene alluvial fan that sprawls across the middle of Oakland, as shown by the “Qpaf” code on the geologic map.

The “Qmt” code is the marine terrace I’ve discussed before. The fan is dissected by modern streams into several lobes, which take their position in today’s cityscape as distinct topographic hills as seen in Google Maps topography:

Bella Vista hill lies in the polygon defined by Park Boulevard, East 34th Street, MacArthur Boulevard, 14th Avenue, East 18th Street and 8th Avenue. All of those street run in valleys or saddles, except that East 18th is on a break in slope. The numbers refer to the following photos, taken from across or in the valley of 14th Avenue Creek.

The hill is low on its bayward side, as shown here from E. 22nd Street.

It has a corrugated surface, such that 9th, 10th and 12th Avenues run on high ground and 8th, 11th and 13th run up declivities. Higher up on the hill, the ground is steeper and the allee of palms marking the former Francis Smith estate is the defining feature of the hill.

The top of the hill has two eminences. The more dramatic one is on the south where Highland Hospital frowns down upon the stream valley.

Hospitals, like schools, were traditionally sited to take advantage of fresh air. Highland Hospital took its very name from this practice. Here’s a view of the whole hospital complex on the southern boss of the hill.

The northern knob is higher, exceeding 200 feet elevation. At its high end, 10th Avenue becomes Bella Vista Avenue and curves across this peak. Old palm trees from the Smith estate mark it from a distance.

Borax Smith knew what he was doing when he picked this hilltop for his home base. The hills on the fan to the south are a bit higher, but the views to every other direction were unimpaired from that spot. If you want to walk the crest of this hill, go up 10th or 12th Avenue and jog across to 13th and take it all the way up to the I-580 overcrossing.