Archive for the ‘Franciscan rocks’ Category

On Pryal’s quarry

21 January 2019

As I find the time (or as the subject hijacks me, in this case), I sniff around for details of Oakland’s rock quarries. There are a good two dozen of them. One I’ve always been curious about first appears in 1868 in The Natural Wealth of California, by Titus Fey Cronise: “The quarry from which the stone used in erecting the Deaf and Dumb and Blind Asylum was obtained, is situated on Pryal’s ranch, about four miles from Oakland. The supply of this stone is exhaustless.”

First thing was to find Pryal’s ranch. Andrew Dewitt Pryal (1832–1907), universally known as “A. D.,” had a spread in Chabot Canyon, the valley of Temescal Creek below the Lake Temescal dam. It was a thriving nursery that Pryal had started back in 1853, on land just upstream from Vicente Peralta’s reserve. Here it is on the Henkenius map of 1888, which has the arc running across the middle representing four miles’ distance from City Hall. It also labels the streams; Harwood Creek is called Claremont Creek today.

That map isn’t lined up with true north, so let’s be more systematic. The next set of maps all cover the same area. Here it is on the Dingee map of 1884:

and in Google Maps today:

So the Pryal ranch was on First Street, now Chabot Road, in the bottomland now occupied by Clover Drive, Chabot Court, Patton Street and part of the Chabot Elementary School grounds. Can you see what caught my eye? It’s that excavation on the north side of Chabot Road east of the hill, or what looks like one. There are so many quarry pits around.

Here’s a photo of the old ranch from the 1897 book Athens of the Pacific:

and roughly the same shot today, from farther east and higher up at the end of Margarido Drive:

Pagoda Hill got its name from the eccentric mansion built on its crown by J. Ross Browne. The young eucalyptus grove was typical of the time; Californians had been planting various Australian species for many years. Later a subdivision of Browne’s land was named Eucalyptus Hill, and Eucalyptus Road runs through it. There even seem to be a few trees left from that grove.

Anyway, back to the quarry. The original Deaf Dumb and Blind academy was a gorgeous thing built of an excellent “blue granite” that unfortunately was all discarded after the school burned down in 1875 and was rebuilt with a different plan. All “blue granite” means in this context is a hard stone with visible grains and no lime. And now we can look at the geologic map of the Pagoda Hill area.

The hills are made of Franciscan melange, a body of mostly metamorphosed sandstone and shale (argillite) with various-sized lumps, or knockers, of things like basaltic lava (fg, for greenstone), chert (red blobs) and serpentine rock (blue).

Here’s what’s over there. At the top of Roslyn Court, right under the big “J”, is greenstone. It’s shot with calcite veins and would never be picked to build a structure.

On Roanoke Road, the street between the “m” and the red blob, there’s mostly hard sandstone of the type customarily called “blue rock” by local quarriers.

I concluded, from a close-up look at the contours of the land and the general lack of decent rock, that there was no quarry here. It would have been one of the largest quarries in the county, supporting decades of production, but there’s no record of such a thing. This was just your usual digging and grading for a housing development.

So where was Pryal’s quarry? On the south side of his property. I remembered a photo displayed during an Oakland Heritage Alliance walk in Chabot Canyon: a shot looking across the valley along the old train trestle, and on the bare hills opposite was the high, rugged face of the abandoned Berkeley Rock Company quarry. I did my best to reproduce that photo by standing on the old grade, next to the top of Reata Place, and looking southwest. The quarry scar, as I recall the old photo, was at upper center about where the heavy cable passes in front of a house and lamppost.

That’s the rock face on Broadway, between Brookside Avenue and the Margarido Stairs, where three new houses were inserted about 10 years ago.

California State Mining Bureau Bulletin 38, from 1906, says about Berkeley Rock’s operation: “The deposit is a much altered trap-rock, and is used for concrete, macadam, and gutter rock. The company produces about 250 yards a day.”

I conclude that Berkeley Rock was working a cut that Pryal had opened 30 years earlier. That Pryal’s quarry produced enough good rock for a large stone building was a lucky accident, because the melange zone is a plum-pudding of mixed rock types.

The Berkeley Rock quarry made news during its years of operation, which started in 1902. The quarry’s 10-acre site was in the way of the Broadway extension, and a lawsuit in 1905 established that the road would go through. On 18 July 1906, an unknown dastard booby-trapped the quarry’s main engine with a package of dynamite, gravely injuring Frederck Hoffman, the superintendent. They used to call such criminals dynamitards. Another dispute over the quality of the company’s stone led to gunfire later that year. The company continued in business, however, for a few more years until the Oakland and Antioch Railway established its right-of-way through the property in 1911 and the Broadway extension was finally pushed through in 1915.

The homes in the old quarry have some rocks lying around. More Franciscan “blue rock.”

This tale still leaves a mystery. Cronise’s book also contains this interesting passage: “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.”

Gold is otherwise absent in the East Bay, as far as I know.

The lavas of Easter Hill

10 December 2018

It all started in the Oakland History group, on Facebook, when someone posted an image from a glass-plate negative for sale on eBay: a road-building crew at work somewhere in the East Bay hills. Was it Oakland?

We quickly determined the view overlooked the area that would become Richmond, but what was that little round hill in the rear center? It was too large and rounded to be a shellmound. It must have been bedrock; however, modern maps show nothing like it. But Andrew Lawson’s geologic map of 1913 did — an outlier of Franciscan lava at a locality named Cerrito.

The 2000 geologic map shows it too. Incidentally, I love the old map because it shows that Potrero San Pablo, the rocky ridge on Richmond’s west side, was essentially an island a hundred years ago.

The handsome little hill of Cerrito was called Easter Hill, because it was popular for Easter sunrise services once upon a time. Photos in Calisphere’s Richmond Local History Photograph Collection show it in about 1910:

and in 1912, behind the Stauffer Chemical Company plant, which used to process sulfur-bearing ore from mines in the Oakland hills:

The hill was laid out with roads and called El Cerrito Terrace at the time, but apparently never got more than partially settled before the World War II years because the Kaiser industrial combine acquired it for a quarry, to help fill in the marsh and build the tremendous shipyards of Richmond.

And that was pretty much the end of Easter Hill the hill, but in the 1950s the site became a pathbreaking low-income housing development, Easter Hill Village. After a few decades the neighborhood had gone sour and the buildings had deteriorated, but in the early 2000s Richmond renovated part of it, added new small multifamily homes and renamed it Richmond Village.

I had to go see if the rocks were still there. They are! Take the 23rd Street exit from 580 west and go right on Cutting Boulevard for two blocks, then right on South 26th Street.

Remnants of the hill add topographic interest to the site, and large boulders from the old quarry are placed all around.

Those boulders display a variety of igneous textures and rock types that’s remarkable in an exposure so small. There’s fine-grained, vesiculated (bubbly) andesite.

There’s lava jammed with centimeter-sized feldspar crystals (phenocrysts).

There’s lava ground into fragments by movements of the hot lava around it (autobreccia) — actually two kinds of autobreccia, hot and cold.

I wasn’t sure that all of these came from the same body of rock until I saw them all in one place, packed cheek by jowl in the same outcrop.

But wait there’s more — a textbook-quality outcrop of pillow lava.

Close up, the pillows look almost as fresh as the day they squeezed their way red-hot onto the seafloor and froze in this distinctive form, the outcome of cold water playing whack-a-mole with rising lava.

If you make your way to the hilltop, the rock is kind of punky but the views are inspiring whether you’re looking west, southeast or southwest.

So Easter Hill is still an excellent place to geologize. The village seems like a good place to live, too.

The Dunsmuir-Chabot trail

1 October 2018

The most remote part of Oakland will be opened to public access fairly soon, when the East Bay Regional Parks District finally gets around to constructing a trail between Dunsmuir Ridge and Lake Chabot. I made my way into part of the route a few weeks back. It’s interesting and inviting territory, set above an untouched oak-filled stream valley with Fairmont Ridge beyond.

The land has divided ownership, with parcels belonging to the city, EBMUD and the East Bay Regional Parks District. They’re all public agencies, so the bureaucracy must have been difficult. Here’s the setting, as laid out in a 2009 EBRPD map.

The solid blue line is a trail in Anthony Chabot Regional Park that’s been closed for years. The dashed blue line is the proposed Dunsmuir Heights to Chabot Regional Trail.

This summer the EBRPD board was shown this map of the approximate route. Again, the solid line is an existing (deteriorated) roadway and the dashed part will be built from scratch. The photo at the top of this post is the view from the EBMUD water tank at top center. The part I’ll be showing is between there and the “P” mark at the city golf course.

A couple more maps to help you see what’s here. First is the bare land as shown in Google Maps terrain view.

The centerpiece of the trail’s route is the valley in the lower right quadrant. Note its depth and steepness. The permanent stream in that valley has no formal name, so I will hereby dub it Chabot Creek. And finally here’s the same area in the 1947 topographic map, which shows the old roads that will become the trail.

If you look at the upper part of Chabot Creek valley, you’ll see it turns sharply from southeast to southwest as you go downhill. On the Google map, though, the streamcourse is interrupted by a flat area. That’s landfill made of waste from the Cypress Viaduct, which collapsed in the 1989 earthquake. It’s sterile and weedy, but the view is nice.

At its edge is a curious structure, visible in Google Earth, that turns out to be a spillway, made for the event of a large rainstorm during a very wet winter. Presumably the landfill was capped with a layer of clay to stop any contaminants from leaching into Chabot Creek, and thus the site would fill with rainwater quickly and have a risk of spillover.

If you looked closely at the second map, you saw the intriguing pointers to an “old foundation” and a “1936 WPA rock chimney.” The chimney is a massive stone fireplace, suitable for a hunting lodge. But the building it once occupied is gone. Foundations around it show that it was a group facility of some kind. I’m hoping that local historians can say more about it in the comments.

A stone in the entryway is carved with the date 1935, so the map is slightly in error.

In any case, the stonework is indeed classic WPA masonry, of the same vintage, material and durability as the Woodminster Cascades in Joaquin Miller Park.

And speaking of stone, what are the rocks like around here, you ask. Here’s what’s mapped in the area.

“Jsv” is the Leona volcanics, “KJk” is the sedimentary Knoxville Formation, and the blue field is Franciscan melange, the same body of rock underlying Knowland Park. When I visited, I checked out a roadcut right where the Franciscan and Knoxville meet and found an assortment of rocks.

All of these are appropriate for the Franciscan, but the brown sandstone could just as easily be from the Knoxville. A return visit is in order during the upcoming wet season, when the ground is firmer. I hope to see more signs of the Franciscan “knockers” so well exposed in Knowland Park — and on the golf course, like this blueschist knocker cropping out in the rough.

The plans for the Dunsmuir Heights to Chabot Trail are supposed to come up for public comment this fall, with the work to be completed by 2021.

Franciscan landscaping

9 July 2018

This house in Piedmont caught my eye not long ago. Homeowners who live in conspicuous places do their neighborhoods a service by making their properties shine. I appreciated the care the owners of this home displayed not just in their plantings, but also in their choice of rocks.

The site (110 Scenic Avenue) is in the middle of the block of Franciscan sandstone that underlies most of Piedmont and some adjacent parts of Oakland. The massive sandstone, of an unobtrusive tan color and undistinguished structure, makes a serviceable setting for some of the Franciscan’s other, more colorful rock types.

The exposure of bedrock is discreetly patched with concrete, which may well conceal rock bolts set into the hillside. The section of concrete on the right side, below, is surfaced with the same blue serpentinite found at Elks Peak in Mountain View Cemetery, the old pit at Serpentine Prairie, around Butters Canyon, and elsewhere.

There are several basins built onto the exposure. The bluish high-grade metamorphic river rock is carefully chosen, too. It comes from outside the Bay area, most likely somewhere on either flank of the Sacramento Valley.

And just beneath it is this little jewel of high-grade blueschist.

Of course a geologist’s first focus is on the stone. But the true beauty of a yard like this is how the rocks converse with the plants set among them over the course of a California year. I’ll be back to see that.