Archive for the ‘Oakland rock types’ Category

The changing identities of the Leona Quarry

9 November 2020

Last week I finally gave in and returned to the high hills — for exercise, as permitted by the county health authorities — and couldn’t resist a reconnaissance of the Leona Heights area. It’s Oakland’s boldest and most rugged region. Here it is from Knowland Park, above the zoo.

Most Oaklanders may know it, though, as the mountainside with the huge scar on it overlooking I-580, the former Leona Quarry.

The quarry was first opened by the Ransome-Crummey Company in 1904 and ended operations under Gallagher & Burk in 2003, but it changed hands (and names) several times over the years, making its detailed history hard to trace. Also, newspaper accounts often confuse it with the Leona Heights quarry, which was at the site Merritt College occupies today.

The quarry was first made feasible by an extension of the Laundry Farm railroad, above Mills College. It was originally high up a steep grade, as shown by the pick-and-hammer symbol in the 1915 topographic map.

I believe it was up there because the bedrock was well exposed, making excavation unnecessary at a time of heavy reliance on hand labor. The 1947 map shows that operations had moved downhill, and quite a bite had been taken out of the hillside.

And the 1980 update of the 1959 map shows the quarry scar at its ultimate size.

The whole time, this hillside was being quarried exclusively to make crushed rock. There was a huge demand for coarsely crushed stone in the days before asphalt and concrete pavement. The gold standard for city streets in the late 1800s and early 1900s was macadam, which has completely disappeared since then. You’ll only see it in silent movies.

A macadam road started with a shallow excavation that was filled with several layers of crushed rock, of successively finer grade, topped with fine gravel or rock dust. The jagged, blocky texture of crushed rock made macadam roads exceptionally firm in comparison to plain dirt or gravel, and they didn’t turn to mud in the rainy season.

As Oakland grew, filling in the harbor and airport and covering East Oakland with suburban tracts on an ambitious street grid, its quarry owners prospered, especially the well-connected ones who could arrange favorable contracts and keep wages low. Plain old crushed rock — road metal — was in high demand. Although there were still good markets for crushed rock after the macadam era ended, things were not the same. The Leona Quarry outlasted all of its competition in Oakland thanks to its remote location, good rail transport and ease of production. But eventually the city expanded to the quarry’s doorstep, the quarry ran out of easy rock and the show ended in 2003, when I took this shot of the north end of the property.

That’s when the site took on its next identity — a townhome district. The rock no longer matters.

But it used to. I think the Leona Quarry started running into problems as the standards in the rock business grew steadily stricter.

Leona Heights, the mountain, consists of a body of much-altered volcanic material of Jurassic age that I refer to on this blog as the Leona volcanics. Its eventful history left it impregnated with pyrite, iron sulfide, in many places. A little farther northwest, in the valley where route 13 splits from I-580, there was enough pyrite to support at least two mines. Down at the Leona Quarry there wasn’t as much, but it does exist and, as it does in the old mines, pyrite decays in the air and rain into iron oxides and sulfuric acid. The oxides turn brown, staining the Leona volcanics this typical color.

They also stain the stream water, as seen here in the headwaters of Chimes Creek above the quarry (and elsewhere in the hills).

The west side of the quarry was full of this “red rock” while the east side consisted of a dense blue-gray siliceous rock, more like this specimen I collected there back in 2009.

Whereas the red rock was useless for things like concrete aggregate because of its pyrite content, this was the good stuff. Nevertheless, the market for excellent road metal came to be dominated by huge outfits like Granite Rock — whose co-founder, Arthur Roberts Wilson, started his career at the Leona Heights Quarry back in the 1890s.

Meanwhile today, the former quarry is now a townhome plantation, set at the bottom of a high, steep rocky bowl.

There is no guarantee that the quarry’s second identity will last forever. Fire, earthquake and rockfalls can overcome any defense given enough time (although the Leona Quarry development has a GHAD that maintains the defenses). Zoning changes and real-estate fashions can undermine such enterprises as surely as physical hazards. There is no guarantee that anything we build will last a century, like the quarry did. Like the ancient philosopher said, everything flows.

Upper Indian Gulch

26 October 2020

When I last featured Indian Gulch on this blog, it was about the easy part, mostly a stroll up Trestle Glen Road. It ended with this glimpse of the living Indian Gulch Creek, bounding down the rock slopes of the Piedmont crustal block on its way to culverted oblivion beneath the elegant Trestle Glen neighborhood.

Upper Indian Gulch lies within Piedmont and the west fringe of Montclair that looks down upon Piedmont. Nowhere is the creek up there accessible to passers-by; if you want to see it you have to buy a house whose lot includes it, or make friends with someone who owns such a house. You’ll have to imagine it running in the dark underneath the street, as it does along La Salle Avenue just above St. James Drive.

Here’s an overview of the upper creek from Google Maps terrain view. The creek has three branches; the west fork is the main branch. To be a stickler, that fork should properly be called Indian Gulch Creek and the other two are just tributaries. The old property line between the two middle Peralta ranchos ran up this valley, Vicente’s on the left and Antonio’s on the right. Later the same line separated the Oakland and Brooklyn Townships of Alameda County. Today neither the ranchos nor the townships are relevant any more, but the boundary influenced the pattern of land ownership a century ago as Oakland expanded its territory and developers shaped the outskirts.

A stroll here is a workout. Part of my Ramble 4, Uptown to Montclair, goes up the creek’s middle fork but the steepest part is pedestrian-unfriendly. Three years ago I featured an excursion into the valley of the east fork. That pretty much exhausts the possibilities in those two valleys. In the west branch, two dead-end roads will take you to the floor of the valley, though the creek is not accessible. Indian Gulch Road leads down from Glen Alpine Road, just above the word “West”:

And Calvert Court swoops from Blair Avenue down into the creek’s highest watershed, where Oakland’s most isolated properties lie.

Here and there, you can get a look at the bedrock under the watershed: sandstone and mudstone of the Franciscan Complex.

And it’s hard, on Piedmont’s winding streets, to grasp the contours of the land. This view across the middle fork at Hampton Park is about as good as it gets.

Really, the best experience of these headwaters is on the rim roads that encircle the watershed. They aren’t photogenic in ways that my camera have caught many times over the years, but the views glimpsed through the trees and past the homes have always pleased my eye.

Looking east-northeast up Hampton Road at Sea View is a good view of the high rim of the east branch, topped by Pershing Drive.

By all means visit Oakland’s best bedrock there.

And don’t miss Wood Drive, along the north rim, where this excellent outcrop of Franciscan metachert awaits.

Indian Gulch is a good candidate for a circumambulation.

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.

Rocks of the Bilger Quarry

6 July 2020

It’s been twelve years since I wrote about the former quarry where the Rockridge Shopping Center sits today. Except for the pond, the whole space has gotten a makeover and it’s time for a fresh look. But first, some nostalgia. Back in 2008 the 24-hour “Big Long’s” was still there. I used to shop there; it had everything.

And flanking it was the big old Safeway with more businesses between and beyond, and the bank in the far corner. I used to bank there.

All of this is now gone, and the site is under intermittent redevelopment. Decades ago this was a giant rock pit, active for more than 70 years, that for a long time was the largest rock quarry in Alameda County. It was started by the Oakland Paving Company in 1870, and the name of Frank Bilger was associated with the succession of enterprises that produced crushed rock here, so it’s usually referred to as the Bilger Quarry. (Bilger learned the trade from his father, a German immigrant, and he surely pronounced his name the German way with a hard G.)

Now the Long’s site is a big Safeway, and the old Safeway and bank buildings are part of an empty lot. Only the water-filled pit on the east side is unchanged, and the walls show no sign of decay, which is a very good thing because it’s right next to St. Mary Cemetery.

The whole quarry site occupies a small body of quartz diorite, an intrusive (meaning it didn’t erupt) igneous rock that’s unusual but not unheard-of for the Franciscan Complex. It’s mapped as the purplish blob in the center labeled “Kfgm.”

It happens to be excellent rock for industrial and engineering purposes. The Tribune in 1890 wrote, “The material used by the Oakland Paving Company is a crushed blue rock, a trap dyke that is practically indestructible, submitting without injury to the hardest usage for eight or ten years without repairs, and with proper care, such as any pavement requires, lasting three or four times longer.”

The east end of the quarry exposes the bluish stuff. This exposure, right behind the Safeway, also has flaky veins of calcite. It’s very tough — not that I’ve used a hammer on it lately, but after seeing lots of rock you get a feel for this.

The west side consists of a much lighter material, a bit coarser grained and slightly less durable.

Between them is a contact zone that I recall as being black and sheared, with mineralization that was probably iron-manganese oxides. It was covered up when the new Safeway went in and parts of the rock face were fixed up for safety. I took this photo in 2018 from the roof parking lot.

There’s chainlink netting on the rock face, just in case it decides to start crumbling onto the roadway.

You’re always cautious about building inside an abandoned quarry, because rocks don’t last forever — that’s why they’re mostly underground, covered with soil. The experts have assured us it’s OK, and I trust them pretty well. The cemetery will last a good long while, and the former California College of the Arts campus, while it looks precarious perched above the other side, has passed muster too and someday will be apartments with good views.

What continues to impress me, every time I visit, is how different Oakland used to be. Throughout the late 1800s, the cemetery on one side and the CCA site (then it was the Treadwell estate) on the other were cheek-by-jowl with this huge operation that blasted three times a day, starting at six in the morning, and employed hundreds of men in producing crushed rock. But back then, rocks were money.