Archive for the ‘Quarries and mines’ Category

Signs of the old Alma Mine

20 June 2022

I devote a chapter of my upcoming book to Leona Heights, where I review the human history of this much-disturbed area and introduce the geologic history of the much-disturbed rocks.

There were three waves of digging in these hills. The Ohlones started it thousands of years ago, harvesting ocher for a thriving regional trade. In 1891, Fritz Boehmer resumed ocher mining in earnest to supply his paint factory. Then the Realty Syndicate, trying to make a few bucks from its vast land holdings, opened a rock quarry where Merritt College sits today. That was in 1896.

Finally Boehmer, whose ocher operation had ended when his factory burned down, found amazing deposits of pyrite ore next to Redwood Road and got into the pyrite business in 1900, opening a mine that he named after his daughter. The Alma Mine produced ore for the next 21 years, one of several pyrite mines in these hills.

Records of those mines are scant and confusing; some appear to have changed names with new owners, and all the shafts and adits (well, almost all) have been sealed. But I’m pretty sure about the Alma Mine: where it was and what it left behind.

Supposedly the first tunnel was dug near Fritz Boehmer’s roadhouse on Redwood Road, which appears to have been where the Lincoln Square Shopping Center sits today. I’m going to show a bunch of maps now. The shopping center’s next to the Warren Freeway, route 13, at the upper left corner of the next two images, a 2006 aerial photo and a blend of the digital elevation model with streets half-superimposed.

The 1915 topo map shows Redwood Road as it used to be, with a symbol where the mine was. It’s where the gas station is today, or under Terrabella Way.

An old-timer told the Oakland Tribune in 1950 that “friction set fire to the ore about 1908. The shaft was blocked off and the company moved operations further around Redwood Road, digging another tunnel to hit the same deposit at right angles.” Plagued by repeated fires from pyrite dust and the mining collapse that followed World War I, the Alma Mine ceased business in 1921.

The next edition of the topo map was issued in 1947, after Redwood Road had been rebuilt, and there was no sign of the mine, or any other structure, from the earlier map.

But aerial photos from the intervening years show what happened. This image from 1939 shows the old course of Redwood Road and the wasteland of tailings left below the first mine site. The second mine entrance was to the east, at the point of the sharp bend in the road. There appears to have been an ore transport line going from there straight southwest down to the old train tracks that used to run beside Lion Creek.

A year later, the area was being rebuilt as a Key Line streetcar route was pushed up Redwood Road, driving residential development past the upper Laurel toward the future Crestmont neighborhood.

This 1947 airphoto shows the new configuration of Redwood Road along with the ghost of the old road. The former mine pit was being mitigated and the new road exposed a lot of fresh rock; at the same time, land was being cleared along the big curve for new structures. (A ground-level photo from 1949 shows the rugged walls of the old pit.)

The 1958 topo map, with updates to 1980 in purple, shows how thoroughly the area was transformed after that.

Which brings us to today. Here’s a closeup of the 2006 imagery with the locations of the following photos I took last week.

The pavement entering Terrabella Way is deeply eroded by acid runoff from the exposed rocks, which are still full of pyrite.

And the iron oxides left behind continue to form fresh ocher.

The 1940s roadcut below Terrabella Place is strongly colored by iron oxides. It’s why this area was rich enough to support a mine.

It will take a long time for vegetation to cover the scene of the old mine.

The pit is really rather deep here. Now it holds the Redwood Reservoir, a big steel tank. I could definitely come back and spend an hour with these rocks.

And then there’s down below, on Geranium Place, where the old mine tailings plus the road construction have left bad ground. That caught my eye a few years ago, and it’s just as bad as ever.

When it comes to mines, especially pyrite mines, the past is never really past.

It’s a bit frustrating reaching the limits of the available information. There are surely other records out there I could consult, but not during a pandemic.

Rocks in the gutter

9 May 2022

Down in the Chinatown and Produce District area, we have some special rock-lined gutters, ranging from fine . . .

to crude . . .

to funky.

They’re the nearest thing Oakland has to cobblestone streets, and they serve the same purpose: heavy duty traffic.

The variety of these gutters suggests that they were emplaced over a long period, under various city contracts. Given that, it’s probable that the stones come from several different sources. But nearly all of them are basalt, the fine-grained, gray to black lava erupted from volcanoes up and down the western states.

These days basalt is a fancy stone, as seen in finer landscapings like the courtyard of Berkeley’s new School of Public Health building. These are natural hexagonal cooling columns of basalt, like those up at Devils Postpile in the high Sierra, cut and polished for elegant seating.

But our gutters are lined with prosaic basalt. And I think some of it came from our own hills. The Sibley Volcanic Regional Preserve includes the grounds of several former quarries that produced basalt rock. In 1906, State Mining Bureau Bulletin 38, The Structural and Industrial Minerals of California, reported on the first of these, the Ransome Quarry: “This quarry is on the Old Fish Ranch road, about 5½ miles from the Oakland City Hall. It was opened in April, 1904. A tramway 600 feet long carries rock from the quarry face to the crusher at side of road. The rock is a fine-grained basalt, and is used for macadam and concrete. Some gutter rocks are sorted out. The rock is hauled to Oakland and Berkeley by wagon.”

Sibley’s lava flows aren’t the enormous, massive ones of Oregon and Washington’s Columbia River Basalt, a genuine Large Igneous Province widely attributed to the hotspot that now underlies the Yellowstone region. The Sibley volcano is a dinky thing with a lot of different deposits ranging from ash beds to proper basalt.

I like to think that a couple workers up there kept their eye on the rock and picked out good bits for this premium trade. I imagine that those are the rough gutter blocks. The later street contracts probably used more economical, higher quality material from farther away, like the North Bay counties or even Black Butte up near Orland.

Nowadays, for better or worse, we keep it simple and use concrete or asphalt, even though the work needs more repairs.

Pryal’s gold mine

3 January 2022

The Gold Rush was a bust everywhere in the Oakland Hills, with one exception. That was a short-lived mine, started in 1864, on A. D. Pryal’s ranch in the northern Rockridge neighborhood. This seems most unlikely at first blush, but the source is Titus Fay Cronise’s unimpeachable book The Natural Wealth of California (1868):

“In 1864, Mr. A. D. Pryal, owner of a large ranch about four miles east from Oakland, discovered a vein of auriferous quartz in the Contra Costa hills, which cross his lands. Some of the specimens from this vein were rich in free gold, and the mine opened under the name Temescal, paid well for a short time, but the dislocation of the strata, a little below the surface, rendered its further working unprofitable.”

The only remotely likely source for such an ore is a small body of highly altered mantle material, called silica-carbonate rock (also called listwanite or listvenite), that was caught up in the Hayward Fault. Long-time readers may recall a post of mine on the subject that involved this same locality. Here’s what the area looks like on the geologic map.

That’s College Avenue running up the left side and Route 24 in purple running along the bottom, with Chabot Road to its immediate north; Lake Temescal is in the corner and the silica-carbonate is the dark blue wedge just north of it between strands of the Hayward fault. When I explored it nine years ago, I bushwhacked up its western edge and found nothing. This weekend, I bushwhacked up its eastern edge.

This part of town has been heavily built upon since Pryal first dug it up, but old photos from (I think) the 1890s show the possibilities. The first shows the Lake Temescal dam and the creek below the spillway. What would’ve been the continuation of Chabot Road (then known as Pryal Lane) runs in front of the white house at the left. The little bridge at the bottom is where the next photo is.

Notice what a mess the hillside is above the dam. Anthony Chabot apparently sluiced it all into the reservoir when he built the dam in 1868. And notice what an erosional mess the streambed is. Nobody cared back then, or nobody downstream cared enough to sue Chabot.


Photos courtesy Bancroft Library via Online Archive of California

What caught my eye was the boulder at center left. Well, first, the streambank behind it looks like fault gouge, the pale powdery dirt that faults make by grinding rocks (and which I documented down at the London Road landslide). Anyway, the boulder at center left looks just like a big slickenside, the scraped-and-buffed surface that faults make by rubbing rocks.

The gist of all this is that a wide, complex fault zone like the geologic map shows could very easily carry slivers of rock from quite far away. And this is little known today, but in the early days there were curious, isolated reports of stones of gold-bearing quartz in our hills. At least two have popped up in my reading, one from north Berkeley and another from Leona Heights. So my hopes were not high as I set out on this traverse, but they weren’t zero either.

It was a real nice day. The streams had water and the ground was pretty firm and quiet. This is looking down at the head of Chabot Road, which was truncated by the freeway long ago. A strand of the fault is mapped there, but the road shows no sign of it.

I found bedrock this time. One bit was deeply weathered Leona volcanics, the same stuff that crops out uphill to the east (pink on the map).

This outcrop looked more like a strongly sheared and altered basalt, not unexpected in the Leona volcanics.

This outcrop, hard to tell; probably more of the same, brecciated.

None of what I saw appeared to be silica-carbonate rock or even leaning in that direction. But that’s what I would expect 160 years after a minor gold find petered out. I’m still not clear on what evidence led the mappers to think such a thing was here at all.

Besides, I was happy to find real bedrock at all during this visit, and there’s still a bit of the territory I haven’t set foot on yet — something for another day. After a long absence from the field, these rocks all looked beautiful to me anyway.

Blair Quarries (not the same as Blair’s Quarry)

6 December 2021

Walter Blair, the first resident of Piedmont, left his name in several places. The quarry he started in the 1850s, now near the foot of Blair Avenue, is now Dracena Park. Everyone called it Blair’s quarry. In the 1880s and 1890s, the amusement park he created in the canyon of upper Glen Echo Creek was a big deal. That was Blair Park.

This post is about the Blair Quarries, and this photo.


From Calif. State Mining Bureau Bull. 38 (1906), slightly massaged

The pit in this photo was the centerpiece of a rock-crushing district on Moraga Road, just above Mountain View Cemetery, that the state mining bureau described in 1906 as “Blair Quarries.” The main quarry was “near the summit of the hill, about 100 yards up the slope north of the road. It was opened in 1901.”

Just ten years before, that same land was part of Blair Park, “the most pleasant outing-place in the bay counties.” By all accounts (and they all seem to be collected at historyofpiedmont.com), the scenic canyon had been turned into a rustic garden fantasyland that included balloon rides, a bandstand, waterfall, garden maze, playgrounds and a “Venetian canal.”

After Blair’s death in 1888, the park eventually fell into the rapacious hands of the Realty Syndicate, which began to devour the valuable chert of the Franciscan melange zone starting in 1901. So Walter Blair had nothing to do with this quarry. At the time this photo was published, the Mining Bureau reported, “The company is opening a ‘blue rock’ quarry, of metamorphosed sandstone, on the south side of the road, and is tunneling in quest of rock for a quarry 50 yards west of and below the larger Blair quarry.” The Blair sandstone quarry, as far as I can tell, was where the Piedmont Reservoir sits today, at Scenic and Blair Avenues. If anyone can confirm that I would be most grateful.

When the city of Piedmont bought the property in 1913, the main quarry was finished. For a time, the Red Rock Quarry worked part of the site. Eventually the pit was filled in, and now the city’s corporation yard sits there. Today, the scene looks like this from the air:

and like this in the digital elevation map.

I think the photo shows the east face of the pit, about 60 feet high, late on a summer afternoon. Twenty men worked there, loading orecarts on at least four tracks. Fortunately, the cemetery hadn’t expanded as far as it has today, so it wasn’t disturbed by dynamite and dust the way St. Mary Cemetery was by the Bilger Quarry.

The odds are that much of the red chert you see in Piedmonters’ yards came from Blair Quarries.