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.

Siesta Valley and the De Laveaga Trail

2 January 2017

Last week I attempted the Rockridge-to-Orinda ramble by a northern route. Was strenuous, but it got me into Siesta Valley, a place I’ve had my eye on for years, for the first time. At this time of year the sun is so low that the light is terrific.

First came the climb up Tunnel and Caldecott Roads, then through Hiller Highlands up to Grizzly Peak Boulevard, a good 1200 feet higher, then down across the Fish Ranch/Claremont saddle, where it looked like this.

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That’s Gudde Ridge, in Sibley Volcanic Preserve, with Round Top on the horizon. The stairsteps in the rock are the huge roadcut for Route 24. Siesta Valley is to my left, over the ridge.

Siesta Valley is watershed land under the control of East Bay MUD, so I made sure to have my hiking permit with me. Not a soul was around, but it’s a good habit. The De Laveaga Trail runs from the top of the valley, at the Scotts Peak Trailhead, along the valley’s north flank. (It’s named for one of Orinda’s founding families — see the comments.) I took the wrong way, going straight down the valley floor on the dirt extension of Wilder Road, which leads to the back side of the Cal Shakespeare center. That meant a steep descent and subsequent climb of a few hundred feet on a pretty wet road, but I saw some bedrock of the Siesta Formation I’d otherwise have missed.

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That included this fine chunk of freshwater limestone, all of which fizzed nicely in acid, just like it should.

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Once I gained the De Laveaga Trail, the views opened up. The basalt flows of the Moraga Formation crop out well here.

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This view looks down the Siesta Valley to its continuation as Wilder Valley, across the freeway in Orinda.

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Siesta Valley is very quiet. City noise and freeway noise are kept out by the contours of the land, and on a lazy weekday afternoon I could see myself having a nice nap.

The trail leads up and over the east wall of the valley at about 1500 feet elevation, then it’s a steep 1000-foot plunge down to Orinda. This is the view north. The cattle pond is there because cattle graze these slopes.

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The sun sets so early here that it gets cold at night. Shaded puddles stayed ice-covered all that day.

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The winter haze obscured the Sierra, but not Mount Diablo and the Lamorinda hills.

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As I raced the sunset, downtown Orinda looked inviting. This is a harsh downhill, though. Uphill would be worse, I think. Nothing to do but try it sometime.

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The verdict: Siesta Valley is a challenge to reach on foot, but that’s your only choice as vehicles of all kinds are forbidden on EBMUD land. It’s an obscure piece of land that requires a permit, but it’s a gorgeous place. With rocks!

2016: Pictures from a good year

26 December 2016

Here are some nice views I enjoyed during the year. These shots are meant for clicking through to see at full size.

In January, I said goodbye to the old Bay Bridge and looked forward to the day when the new bridge offers a superb platform for viewing the Oakland skyline.

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In February, I was captivated by the chaparral high on the face of the Leona Hills.

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In March, I got a good look at Mount Diablo from Wilton Drive, on the edge of Redwood Regional Park.

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In April I was transfixed by the view south from Fairmont Ridge to the hills back of Hayward, an area I have yet to visit.

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I took great pleasure in tramping out my first three “geology rambles” this year. Not every photo was geologically relevant, but this moment from the July day when I first envisioned ramble 3 was too charming to forget.

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And several times this year, I’ve gone to Devil’s Slide to dispose of rocks by throwing them into the boiling sea. But the views in the other direction are stupendous.

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I have enjoyed the hell out of geologizing this year.