Archive for the ‘Oakland stone’ Category

In search of McAdam’s quarry

3 August 2020

Alexander McAdam (1854?-1920s) was a minor character in Oakland’s history who left a highly visible mark in our cityscape. A Canadian farmboy who was orphaned at a young age, he came to California after apprenticing as a wheelwright, and after eight years he saved enough money to buy a farm “at the head of Thirteenth avenue,” according to a short biography by James Guinn in 1907. “He was successful in this occupation, but in the meantime had discovered a sandstone quarry on his property. Upon the sale of his farm he acquired considerable financial returns. Stone from it has been used in many of the largest buildings of Oakland, among them being the Unitarian Church, the last buildings of the deaf and dumb asylum, numerous retaining walls, and for many other purposes.”

This caught my eye because I have long thought that Oakland’s rocks were exclusively used as crushed stone. Yet here in the First Unitarian Church, ashlar blocks of genuine Oakland sandstone form the dignified cladding of this important cultural monument and civic institution, built in the early 1890s under the energetic leadership of a leading Progressive of his time, Rev. Charles Wendte.

Rev. Wendte oversaw the building project from his home across the street. The stone cladding was the costliest item in the project, and he singled it out in his memoirs: “Our employment of stone led to vexatious complications. Quarrymen were unable to deliver this material in sufficient quantities, workmen struck for higher pay in handling it. Contracts were broken or remade.”

I had to track down this stone somehow. The documentary clues are slim, and any signs of the quarry appear to be lost. But first, there is the stone itself.

It’s a fairly sound stone of an even consistency with a warm grayish-brown color and massive (i.e., absent) bedding. The block serving as a lintel over the doorway probably broke during the 1906 earthquake, when most of the cladding along Castro Street and the top of the tower collapsed. (The tower was rebuilt without any stone, a smart move.)

A closer look shows that the stone actually varies (although some of that may be substitute stone from another source, as Wendte’s wording suggests), and that a century of exposure has caused a fair amount of spalling. No wonder there were quality problems during construction.

A still closer look reveals it as a medium-grained wacke (“wacky”): a sandstone with grains no larger than a millimeter and a large component of minerals that are not quartz. The black grains are mostly biotite mica; without a microscope I’m limited in what more I can say.

It’s familiar to me. It’s not the Franciscan sandstone produced by the dozen or so quarries in and around Piedmont. I can rule that out categorically. It’s from the high hills on the far side of the Hayward fault.

All of this is consistent with the documentary evidence placing the source in Montclair. The “head of Thirteenth avenue” is where Park Boulevard, the former 13th Avenue in Brooklyn Township, meets Mountain Boulevard. It’s the intersection at the bottom of this excerpt from the 1897 topo map.

To orient (or disorient) you, here’s the same area today.

The “XII Report of the State Mineralogist,” published in 1894, said the following about McAdam’s quarry: “It is in Medos Cañon, back of Piedmont, and is a small quarry, producing sandstone for rubble and ashler [sic]. It is not worked regularly.” The official who wrote that description, a busy guy on a quick visit to cover the whole county, wrote down “Medos Cañon” when someone said “Medau’s canyon,” meaning the valley of present-day central Montclair where the dairy farm of John H. Medau once lay. I believe that if the site had been in Shepherd Canyon, his informant would have said so as that name was in wide use at the time.

All of this means that the quarry could have been a good exposure of the Redwood Canyon Formation, a wacke of Late Cretaceous age, that forms part of the east side of Montclair’s valley along the Hayward Fault. It’s the unit marked “Kr” on the geologic map, below. The lithological description of the unit, and the composition data from Jim Case’s 1963 Ph.D. thesis, are close enough to the stone in the church.

But also likely is the Shepard Creek Formation (Ksc) and even the Oakland Conglomerate (Ko), when you consider that the units are only subtly different, variable in composition and not well mapped despite the best efforts of competent geologists.

In any case, I had a good time visiting these rock units along the Montclair Railroad Trail the other day. There’s a lovely outcrop of the Redwood Canyon Formation above the trail along the route of the recently upgraded powerline, southwest of the word “grade” on the map. That warty weathered surface, reminiscent of the Incredible Hulk’s hide, is one of this unit’s distinctive features.

But the rock there’s not a good match.

Neither is the rock in the landslide at the upper end of the trail.

And just for good measure, here’s a chunk of sandstone from the Oakland Conglomerate. The material is coarser and wacke-er, but again under the 10X hand lens it’s not like the church’s stone.

Nowhere in this area, in many years of visits, have I seen a body of rock big enough and sound enough to support a quarry capable of producing ashlars — not on this side of the Hayward fault. The nearest quarry site is down Park Boulevard where the Zion Lutheran Church sits today, the former Heyland/Diamond Cañon/Bates & Borland quarry on the side of Dimond Canyon. But that produced crushed Franciscan sandstone, something quite unlike McAdam’s stone.

I can only conclude that McAdam found a lucky hillock on his farm and made the most of it, one that’s been obliterated during the waves of development since 1890. And the site of his farm is, as we say, poorly constrained. Even his life dates are fuzzy. But his accomplishments include making a profit from farming, acquiring a large home in Temescal, serving two terms on the City Council in the nineteen-oughts, and equipping an important building with a handsome exterior (despite the vexation he caused Rev. Wendte). I can’t confirm when he died or where he’s buried, so this building surely is his monument.

While I was researching this post, the papers covered a lovely story about how archeologists used advanced geochemistry to pin down the source of Stonehenge’s biggest stones, a peculiar sandstone known in Britain as sarsen. The New York Times version was my favorite writeup, and the hardcore details are in Science Advances in an open-access paper.

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.