Archive for April, 2011

Five more Oakland quarries

28 April 2011

I’ve scrounged through my files and come up with five more quarries in Oakland that I’ve managed to photograph over the years. I’ll show them from north to south. First, of course, is the old Bilger quarry at 51st Street/Pleasant Valley Drive and Broadway, which I’ve featured before on this blog.

bilger quarry

Next we have the quarry in Piedmont that now houses the town maintenance yard, by the ballfield along Moraga Avenue. The little spur street is named Red Rock Road, and the quarry appears to feature some usable shale from the Great Valley Group. But I haven’t dropped by since 2003, and my memory is vague.

red rock quarry

Next we have the old Leona Heights sulfur mine, at the end of McDonell Avenue, which I featured in a discussion of Lion Creek.

sulfur mine

The big old Leona quarry comes next, which I’ve talked about before, once to discuss the site and another time to show the rocks.

leona quarry

Finally, we have a small quarry in Sheffield Village, right on the Hayward fault where the digging was surely easy. Afterward some of those lovely period homes were tucked in there, along Revere Avenue.

sheffield quarry

There are more quarries to be documented; I just need to consult the records and then visit the sites.

Six Oakland quarries

23 April 2011

Oakland, like most growing cities, started its climb to prosperity with the resources it had on hand. Those were land, soil, water, timber and stone. Today we produce no domestic stone. Here are the remains of six different quarries, five in Oakland and one in Piedmont.

sibley quarry

Sibley Regional Volcanic Reserve is a former quarry where the basalt of a Miocene volcano was exploited for traprock.

morcom quarry

The Morcom Rose Garden is said to be a former quarry; that would have been a gravel pit given that there is no bedrock mapped there.

hiller quarry

The Hiller Highlands neighborhood is built around an old quarry where the highly faulted rocks (the Hayward fault is just to the left of this photo) were handy for making crushed stone.

serpentine

Part of the Serpentine Prairie was exploited for rock at some point, probably for fill material.

dracena quarry

Piedmont’s Dracena Park is the former Blake quarry, yielding Franciscan sandstone for aggregate under Oakland’s streets.

franciscan quarry

And the Zion Lutheran church, off Park Avenue, was built in an old quarry where sandstone of the Franciscan Complex was dug for crushed rock.

There are more of these; I just need to sort through some more photos. I think it’s important to source raw materials like stone from nearby whenever possible.

Mountain View Cemetery knocker, the big one

10 April 2011

Since I featured what I called the big set of knockers (or in geology-speak, large competent blocks in Franciscan melange matrix) at Mountain View Cemetery, almost 3 years ago, the operators of the cemetery have opened a new premium section just below and removed most of the trees, unveiling the best rock on the hill. I visited it this evening. It’s still not much to look at unless you’re looking for it.

knockers

It’s mostly pale-green ribbon chert with some red chert. You might say the green rock has undergone a sea change. I’m not one of the experts in the Franciscan, but red rocks, which owe their color to trivalent iron (Fe3+), commonly turn greenish as the iron is reduced to divalent Fe2+, so I take it that this chert has undergone some challenging conditions in the ancient subduction zone that created the mixed-up melange. I find it harmonious.

green chert

Here’s a closeup. Click it for an 800-pixel version.

closeup

Stone like this doesn’t support a lot of life, being low in nutrients, but lichens have a foothold on it, especially where moisture can gather. The eastern, uphill side is like that, and the total impression, stone and sky and place and time, is most pleasing.

view

Again, click the photo for a big version. And visit the “cemetery knockers” category for the whole set.

Old friends in new places

5 April 2011

I paid a visit to Alum Rock Park today, in San Jose just past the far end of the Hayward fault where it joins the Calaveras fault. It’s a lovely place. One thing I found especially pleasing was the historic warm mineral springs, which happen to be confined to the Claremont Chert.

claremont chert

Down here the Claremont is dark, perhaps because of a high carbon content. I don’t think I’ve mentioned it here before, but the Claremont is actually a small part of the Monterey Formation, a very widespread unit of siliceous sedimentary rock that accounts for a large share of California’s petroleum. The carbonaceous material, in combination with its high permeability and the presence of hot fluids in this highly faulted area, probably accounts for the concentration of stinky sulfur springs here. It’s a fascinating place that I’ll be describing in more detail Thursday on the KQED Quest Science blog. But I knew you’d like to know that I raised a little mental fist as I saw one of Oakland’s distinctive rocks here.


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