Archive for the ‘Oakland stone’ Category

Stones of the Broadway Valdez District

8 July 2019

The Broadway Valdez District is a swath of territory, named by city planners, centered on Broadway and extending from 23rd Street up to I-580. The area is undergoing redevelopment at a furious pace. For my purposes, the area will give birth to a showcase in the use of building stone in current architecture. Here’s the first chapter in that story.

Gone are the days when stone was a load-bearing structural material in Oakland buildings. (A few of our older churches survive from that time.) Gone are the days, even, when stone was fashionable for large-scale cladding (see: Kaiser Center’s dolomite and Lake Merritt Plaza’s granite). Today, at this moment, stone is a color and textural accent framing the offset planes of metal and matte components by which today’s designers react to the bland slabs and faceless facings of yesteryear.

First out the gate in the race to develop the Valdez Triangle (framed by Broadway, 27th and 23rd Streets) is the Hanover Company’s two big residential properties, Hanover Northgate and Hanover Broadway.

Hanover Northgate stretches the length of Valdez between 24th and 26th, and its exterior has two different treatments. Here’s the south end.

The part on street level is faced with stone. The blond stuff, which echoes the top level, is an interesting fossiliferous marlstone. And I mean, fossiliferous.

Marlstone is not your traditional white or gray limestone; it owes its hues to clay minerals mixed with the carbonate minerals that define lime rocks. The variegated texture and color is integral to its charm. Notice among the cross-sections of fossil bivalves is a little brown gastropod shell.

Beneath this, at foot level, is a dark gray marlstone.

No obvious fossils here, but there are veins of calcite to lend visual interest. Carbon, not carbonate, provides the black color. Such a rock forms in anaerobic settings, where organic carbon is reduced to elemental carbon rather than being oxidized to form carbonates or CO2 gas.

The other end of the Hanover Northgate has a different palette: a warm buff-gray over a crystalline black footing.

In between the two parts, the carport features this rugged paving. However, it’s just dark-tinted concrete — cheaper than stone, just as tough and more controllable.

On to the real stone: a nicely polished laminated limestone. This panel displays two little faults cutting vertically through it; the middle part has been displaced upward. There’s also a thin vein, the result of a later fracture.

Interestingly, all the panels I took a close look at appeared to be placed stratigraphically upside-down.

One of the first things a geologist looks for is evidence of stratigraphic up and down. After seeing a few hundred outcrops, doing that becomes automatic, especially in the Oakland hills where many of the steeply tilted rocks are overturned past vertical. Sometimes the evidence can be quite subtle. The most obvious sign in this example is at bottom center, where the thin beds sag into the gaps in the thick bed. This rock — in this panel anyway — accumulated in the downward direction.

If I’m right, then the stone supplier made sure to mark this stock with arrows so it would be set in a consistent direction. Although the result might confuse geologists, it would avoid giving observers of the walls, even ordinary folks, a vague sense of disorder.

The dark rock at the base of the wall is “black granite,” better known to geologists as something like amphibolite or gabbro. It has a sandblasted finish for a more matte appearance.

Between the two Hanover buildings is a lovely plaza, open to the public and graced with stainless-steel sculptures by HYBYCOZO: a stylized oak tree and eight California poppies.

Not much stone is in evidence — the plaza is mostly tile and concrete and metal. But the benches are topped with solid black basalt.

Which leads us to the Hanover Broadway building, soon to have a Target store on the ground floor.

There’s not much stone on this building either. Like “Whistler’s Mother,” it’s a study in black and gray. Here’s an odd irregular panel on the side facing the plaza: brecciated limestone.

Here’s a closer look at this intricate material. (All images click to 800 pixels, as is my usual practice.)

And around the side in an entryway are some panels of gneiss, complete with quartz veins. The squashed-and-squeezed veins feature what are called ptygmatic folds, because geologists have come up with the damnedest words for things.

These stones, all of them, are things no human artist or artisan can duplicate. Though it may go in and out of fashion, stone will never go out of style.

Oakland buildings clad in stones

4 February 2019

One of the cool things about Oakland is its huge variety of buildings, dating from midcentury — mid-19th century, that is — to brand-new. There’s a particular variety of midcentury-20th-century architecture that’s piqued my geological interest: boxy tilt-up structures that I think of as Old Period Safeway, with a cladding of natural rock. In 2017 I showed an example of the type clad in beautiful serpentinite, so I set out to find others around town.

The sharp-eyed folks in the Oakland History Facebook group pointed me to several candidates, and I took an afternoon to visit them and also cruise much of the main roads by Zipcar. Yesterday afternoon I took one more little outing to capture the distinctive building of KP Market on Telegraph Avenue, the best pan-Asian grocery around.

The stone cladding covers only part of the front, and besides it’s painted over. To see it pristine you have to go around the side and look along the base of the wall, where taggers never venture (and thus paintovers aren’t needed).

This is the same coarse-grained dolomite rock used on the iconic Kaiser Center building.

Now for some genuine Old Period Safeways, but first a lament for rocks that get painted over, which permanently spoils them. The former Safeway on San Pablo at 27th Street, for instance, has lost its original appearance beyond retrieval. Without the colors and lusters of natural rock, the walls are unappealing.

But the former Safeway on upper Golf Links Road, in the Grass Valley neighborhood, is unspoilt.

Close up, it resolves as a mixed metamorphic assemblage of river rock, perhaps from the northern Coast Range but the presence of granite amid the sandstone says Salinian instead; that is, from the Santa Lucia or Gabilan ranges around Salinas. I don’t know for sure, it’s just fun to guess.

Another former Safeway, on 14th Avenue at E. 17th Street, still has its stones out.

This wide-ranging river-rock assemblage is darker and more rounded, and granite is absent while lava is present. I peg it as coming from the Diablo Range, but I warn you I could be totally wrong.

There’s one more former Safeway, a dialysis center on Claremont at Clifton, whose cladding still looks good in Google Streetmap but I haven’t visited it yet. The rest of our old Safeways, and there were about 20 listed in the 1969 phone book, are either gone or have been renovated or didn’t use the rock cladding.

One more supermarket and I’ll move on: the Cardenas grocery on High Street.

The cladding on the front side is painted, but on the side you can see it’s an excellent quarry-crushed golden quartzite mixed with lava and what might be travertine or sinter. I’m thinking the northern Sierra here, but that’s a long way to ship crushed rock, even fancy stuff.

Couple more notable buildings, non-Safeways, to show you. Next to the Post Office building off Hegenberger is a low-slung office building, 8475 Pardee Drive.

It’s clad with a selection of river rock I don’t hesitate to call Franciscan sandstone, maybe from Sonoma County.

Finally there’s the Community School for Creative Education building, on International at 21st Avenue. Something about the whimsical accents and the warm, even-textured cladding makes just the right impression.

This stuff is straight crushed quartzite that’s gotta be from some special place in the Sierra foothills, if not farther afield.

Material of this quality can last for centuries, if well maintained.

One cladding type I didn’t seek out for this post is pretty common: big flat hunks of undressed sandstone — that is, flagstone. I have no idea where the stone might be quarried. Some well-known Oakland buildings use it:

But it can be overdone, bringing to mind another fashion, a late-century one: shag carpet.

My knowledge of architecture and the building trades is pretty scant, so if you know the correct terminology for these features, please add an informative comment.

Serpentine and pebbledash on Broadway

22 October 2017

The intersection of Broadway and 20th Street features strong buildings on all four corners. We all know the I. Magnin building (built 1930) and the Capwell (Sears/Uptown Station) building (built 1929) facing it. Across Broadway, we have the metal-clad urban spaceship of the Kaiser Permanente Division of Research building (built 1982) and finally the dark cube of the Golden West Tower Building (built 1968).

One of the nice things about taking the bus is that while you wait, you can look around like architects and urban planners do, as if the cityscape were a stage set. And so, waiting for the 33, I finally took notice of the building wall that I’ve walked past hundreds of times.

It’s chips of dark serpentine, embedded in cement and polished. People in the building trade must know exactly what this is called, but I can’t crack their code. Here’s a closeup.

So all this time, the Golden West Tower Building has been giving the serpentine-clad I. Magnin building a nod, a salute, a shoutout, a heart-tap. I thought that was cool.

That day the 33 took me to Piedmont, where I recognized the same material in Bufano’s “Bear and Cubs” sculpture in Crocker Park, featured here previously.

The other element in that Broadway streetscape is the sidewalk. You’ve all seen it.

This is what’s called a pebbledash finish. Concrete is laid down, then pebbles are pressed into it. When I look at it I think, “What a lovely Franciscan color scheme,” because the reddish and greenish mixture of metamorphosed argillite and chert is so typical of our coastal Northern California rocks. I also think fondly of the red-and-green gravel of Rodeo Beach.

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.