Archive for the ‘Old quarries’ Category

The Dunn-Spring Quarry, north Berkeley

27 November 2017

Glendale-La Loma Park, a little ballfield/playground complex in the north Berkeley hills on La Loma Road, is a repurposed quarry that’s had a true Berkeley history. The original quarry, operated by J. J. Dunn, appears to date from 1892. John J. Dunn, a Canadian immigrant born in 1839, was a major contractor in California building roads and sewers starting in the 1870s. This is Dunn portrayed in 1896 in the Oakland Tribune.

In 1900 Dunn advertised the quarry for sale “on account of sickness,” and died of Bright’s disease (kidney failure) in St. Helena that June.

In 1904 the Dunn quarry was reopened by Louis Titus, former head of People’s Water Company, as part of the Spring Construction Company. Its dawn-to-dusk blasting operations infuriated local residents, who obliged it to shut down in 1909 by threatening the business-friendly city council with a recall campaign. The company made the gaslighting claim that they were not operating a quarry, even though the rock from the pit was being used for streets and homes in the Thousand Oaks tract, but were in fact building a reservoir for the People’s Water Company.

After its abandonment the Spring quarry became an attractive nuisance, drawing generations of youngsters to its steep sides and deep swimming hole. Even those who didn’t swim in the cold, murky groundwater must have enjoyed the view.

In 1950 an 11-year-old boy drowned, and the city fenced off the quarry. The city acquired more property around the site in 1957, and eventually it became what you see today.

Unfortunately I have found no details of the site’s geology, although Titus called it a basalt quarry. The geologic map shows the downhill side as basalt of the Moraga Formation and the uphill side as the conglomeratic Orinda Formation.

This is the basalt. The brownish streaks are slickensides — friction marks from faulted fractures.

Other volcanic rocks here include rhyolitic tuff, a minor component of the Moraga Formation. It’s distinguished by its light color and broken (brecciated) texture.

Superficially, it resembles the Northbrae Rhyolite that makes up Grotto Rock Park and its sister parks, but unlike that heroically strong stuff it degrades quickly when exposed at the surface.

At the foot of the cliff you’ll find pieces of this excellent conglomerate from the Orinda Formation.

But the fact that it has crumbled down the cliff and will fall apart in your hands means that the rock face would be treacherous climbing. The city should be more forthright in discouraging climbing here; instead they just say “check out the other Berkeley parks with rock features…” Stay off it, and if an earthquake strikes while you’re standing there, jump back fast.

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Orinda’s 1204 Hill

30 October 2017

As far as I know this hill has no name, but it’s a highly visible part of Orinda. You pass it on Route 24 between the Wilder exit and downtown, as seen in this Google Maps perspective view. The USGS topo maps give it an elevation of 1204 feet, so I’ll call it 1204 Hill.

It’s part of San Pablo Ridge, but the west branch of San Pablo Creek cut a deep gorge through the ridge while it was being uplifted, forming a classic water gap. That’s clear to see in the 1915 topo map, made before anything significant was developed there.

During the mid-20th century, at least four quarry pits ate their way into this hill, one on the north side and the others on the south. Now it provides a bit of seclusion to the exclusive luxury Orinda Wilder development. I paid the hill two visits this month, and to me it offers seclusion from Orinda Wilder. Here it is, as seen across Wilder Valley last summer.

A fire road encircles the hill for your visiting convenience. It offers good views all around. This is looking north across 24 to grassy Eureka Peak along with wooded Vollmer Peak behind it. Both are also part of San Pablo Ridge.

And in the other direction is the last, southernmost lump of San Pablo Ridge, separated from 1204 Hill by another branch of San Pablo Creek.

Looking west, Route 24 approaches the wall of the Oakland Hills. Eureka Peak, at the right edge, and 1684 Hill on the left, part of Gudde Ridge, form the sides of Siesta Valley.

Both peaks are made of the same lava of the Moraga Formation. The formation is folded like a taco shell under Siesta Valley, a geological feature called a syncline, and hey why don’t we look at the geologic map now. This is the same area shown in the topo map.

“Tmb” is the basalt lava of the Moraga Formation — the taco shell — and “Tst,” the Siesta Formation, is the filling. That red line with the little arrows is the axis of the syncline. The light-yellow unit “Tms” is sedimentary rocks, also in the Moraga Formation, that were laid down between eruptions of lava. To the right of the black toothed line — the Moraga fault — the rocks are much younger and I won’t mention them again.

The quarries were excavating freshwater limestone from the Siesta Formation, used to produce cement and soil amendments, and basalt from the Moraga Formation, used for crushed rock. Here’s the lava.

Where lava flowed onto wet ground, the underlying clay got baked and the steam oxidized the lava, turning both materials red. It’s not always easy to tell what’s what.

There are bits of light-gray limestone here and there. You can tell by the way a drop of acid fizzes vigorously on it. I didn’t take a picture, but I did stop to shoot examples of mineralization in the lava. They might be copper compounds, or phosphates, or several other possibilities that aren’t easy to identify just by eyeballing.

There’s also a little conglomerate that looks for all the world like the Orinda Formation. It goes to show that a geologic map is a simplification of a wacky, complicated Earth. However, I don’t quite trust the stone because it’s loose, not a proper outcrop.

Climbing the hill from the fire road is a scramble. There are only subtle trails, the kind that deer make. But on top of the hill there’s the stubs of a former water tower, and a stone spiral with a little cairn at the center, the kind that locals make. And outcrops.

The last thing to mention is the quarry scar. It displays the structure of the Moraga Formation nicely.

But the exposures are unapproachable and dangerous.

I’m not sure what the developers plan to do with this hill. Probably nothing except watch it closely. The closest street to the quarry scar has home sites only on the far side of the road, and there’s a wide ditch between the road and the quarry that will catch falling rocks.

I’m gonna keep my eye on this interesting spot.

South Dunsmuir Ridge

29 May 2017

I finally got to a sweet corner of town last week, the sunny side of Dunsmuir Ridge, this lovely hill in the Google Maps 3D view.

The view is to the north-northwest, such that the Hayward fault runs straight up about a thumb’s width from the left edge. The maps below start with the 1915 topo map, in which the ridge’s top is the lobed outline of the 625-foot contour.

That straight creek valley along the hill’s south side — the gorge in the foreground of the top image — keeps catching my eye, but it seems to be inaccessible, which might make it Oakland’s wildest piece of land. The watershed map below may help in visualizing the hill and its surroundings. The two black dots are where the fire trail I took starts and ends.

Dunsmuir Ridge is city land, rescued from development after several aborted attempts to put high-end estates on this broad hilltop overlooking (in both senses) the deadly Hayward fault. The fire trail starts at the end of Cranford Way and winds up the ridge to join the fire road from the other side, which I’ve featured here before.

The walk is very scenic. To the north, downtown rises against Mount Tam.

Or if you prefer, there’s the new profile of San Francisco.

Higher up, the view opens out. Here San Leandro Creek is made visible as a line of trees coming out of the canyon toward its mouth near the airport.

But the main attraction is to the south. This is the best place to take portraits of Fairmont Ridge and its quarry scar. Unlike most places, this trail sets off the hill with a foreground of wild, forested land.

The prominent cleared space midway up the trail — a staging pad for firefighters — has regular visitors who find the spot special.

Interestingly, this spot is mapped as a patch of the peculiar Irvington-aged gravel that first brought me to Dunsmuir Ridge in 2009. However, I didn’t notice much of it, if any. See it on the geologic map — the white dots mark the ends of the fire trail.

There are rocks to be seen too. The soil is thin in most places. This little cut displays a profile of the soil and the decaying bedrock — saprolite — just beneath it.

The bedrock varies, and it doesn’t match the geologic map very closely. I would say nearly all of the lower part is not Leona volcanics (Jsv) but San Leandro Gabbro (gb). It has the gabbro’s pepper-and-salt appearance but is stained orange instead of the pristine rock’s bluish gray (as I saw earlier that day in San Leandro). You’ll see it well exposed in the trail itself, where this winter’s heavy rains carved fresh runnels.

If the city fills them before you get there (which it should before they become gullies), there are still roadside exposures that display the rock well, and it’s unmistakably gabbro where the map says volcanics. The top of the hill, though, is unquestionably Leona volcanics.

My long-term plan is to revisit every bit of bedrock in Oakland and log it. Besides sheer nerdery and the chance to improve the map, my motive is to come back to views like this one over and over again.

The old quarry is still for sale. Developers have tried to put houses there, but they keep getting shot down. Better, I say, for the Regional Parks District to acquire the land and develop it for quiet recreation.

Red Rock Quarry

9 January 2017

The Red Rock Quarry was apparently part of the Blair quarry complex in Moraga Canyon, at the west edge of Piedmont on Red Rock Road. Oakwiki reports that it was owned by the Henry Maxwell family (for whom Maxwelton Road is named). The 1947 USGS topographic map shows that the quarry was active at that time.

I took photos of the rocks here last June. The parking lot exposes the rock pretty well.

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The area is mapped as Franciscan sandstone, which underlies most of Piedmont. This locality is near the ancient thrust fault separating the sandstone from Franciscan melange to the east. Being near the fault would have subjected it to a lot of disruption, and that’s what you see here. The rock is somewhat disorganized, with massive beds on the right juxtaposed with thin-bedded mudstone in the center.

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Fractures in the massive sandstone have opened up, filled with carbonate material, then been displaced some more.

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The north edge of the parking lot exposes a nice set of turbidites. These are sequences that consist of beds of mudstone formed by repeated seafloor avalanches, separated by beds of shale that represent quiet times between avalanches.

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Blair and Maxwell made good money here and employed a lot of people. The rock was easy to dig out of the steep hillside, easy to crush without making a lot of wasteful dust, and easy to roll downhill to market. This quarry probably produced plain old crushed stone to be sold for landfill, foundations, concrete aggregate, roadbeds and the like. It was not the more desirable, cherty “phthanite” or siliceous argillite found elsewhere in Piedmont’s Franciscan rocks.

I say “probably” because I couldn’t inspect the whole pit. What I really wanted to do was examine the walls of the quarry itself, which are fenced off.

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They’re fenced off because today the quarry is the readymade site of the City of Piedmont’s corporation yard. As is often the case, this quarry was reused after its initial purpose was gone.