You’ve all seen this quarry, looming over Lake Chabot Street and consuming its approach into Fairmont Ridge. It has an extended historical past, and like all deserted quarries it has an extended afterlife forward.
Seen from south Dunsmuir Ridge
The ridge was first opened up in 1886 by the Stone brothers, Egbert and Andrew, whose father Lysander made his fortune from the wealthy soil of the realm now often called the Stonehurst neighborhood. Their development agency, the E.B. and A.L. Stone Firm, was a wide-ranging enterprise that operated a number of quarries within the Leona Heights space.
By 1918 the quarry was owned by Joseph Costello, and in 1929 it got here into the arms of the newly fashioned San Leandro Rock Firm, which has owned it ever since though operations ceased earlier than 2000.
Right here’s the setting, from Google Earth. The quarry scar is within the higher heart south of the dam at Lake Chabot.
The quarry exploited a physique of rock mapped as basalt lava, of Jurassic age, that varieties a part of the Coast Vary ophiolite. Right here’s the identical space of the geologic map. The Hayward fault is the strong black line simply west of the quarry web site.
Jurassic basalt (Jpb) with San Leandro gabbro to the west, Leona volcanics (pink) and Knoxville Formation mudstone (inexperienced) to the east.
And only for context, right here’s the digital elevation mannequin giving a more in-depth view of the quarry web site and the canyon of San Leandro Creek beneath the Lake Chabot dam, with the energetic strand of the fault proven in pink and older strands in yellow.
Lidar information from Opentopography; fault traces from USGS. Illumination from the northwest.
The boulders that line the entryway are a great pattern of what’s inside. They’re dominated by the darkish, largely featureless basalt.
Right here and there you possibly can spot stream options and glassy areas that help the interpretation of this rock unit as pillow lava, the sort of blobby flows that kind the place red-hot lava meets freezing seawater. Therefore the map image “Jpb” for Jurassic pillow basalt.
The quarry face itself isn’t half as properly uncovered, however beneath the rubble and grass the identical materials reveals up in spots.
The skinny white veins, when you could find a specimen that exposes them, seem to encompass hydrothermal quartz and olive-green chlorite. These rocks went by way of just a few modifications after the basalt first froze.
Extra entertaining is the view over the canyon and the Bay space past. You may see prospects, whether or not you’re a would-be house developer or a would-be park planner.
The planner is the East Bay Municipal Utility District — the water firm — which needs to purchase the land and use the pit to get rid of the soil it digs up throughout trenching. It’s clear grime, so no drawback there; it’s ineffective land for the rest, so no drawback there. And once they’re accomplished, EBMUD needs to make it right into a park. The issue emerges once they spell out the nitty-gritty of their undertaking proposal: “The primary stage contains utilizing trench soils for fill operations for long-term phased placement and stabilization of roughly 3.4 million cubic yards of trench soil on the Quarry Web site over roughly 40 to 80 years.” The issue is all these dump vehicles over all these years on Lake Chabot Street.
The highway that serves the quarry has all the time sparked rivalry. When it was the outdated again highway between San Leandro and Castro Valley, the heavy-duty visitors from the quarry left the dirt-and-gravel highway in tough form. Ultimately the route was paved, however the hillside is precarious and components of it gave approach throughout our newest moist season. All this earlier than the following large earthquake.
The outdated highway was bypassed by Fairmont Drive, a four-lane freeway that was pushed over the ridge within the Nineteen Seventies, however pleasure drivers, commuters and residents nonetheless use it. To protect their quiet byway, the residents have opposed the heavy vehicles of quarry visitors for 50 years, and so they oppose it this time too. As we speak I’m totally on their facet.
A attainable route from the south would attain the quarry by way of Fairmont Drive. It could run up this valley, which is owned by the East Bay Regional Park District and is in any other case unusable as a result of it runs proper alongside the Hayward fault.
Contemplating that the park district and the water firm are two trunks from the identical root, perhaps they might get together with an acceptable easement by way of right here.
