The fault at Roble Road

roblerock.jpg

From College Avenue you can take Chabot Road east, parallel to Route 24 toward the Hayward fault. It passes some exquisite and interesting houses, also the East Bay Municipal Utility District’s main water line, which cuts through the Oakland Hills in a tunnel that has recently been reinforced against fault movement. You also pass right underneath the BART line, on its way to Orinda. But when you get quite close to the fault, Roble Road exits to the north, a one-lane road with a few empty lots from the 1991 fire and a creek running alongside it. Just over the Berkeley line you start to see boulders. This one is at 57 Roble. It’s most likely a large specimen of Leona Rhyolite, but I’m not yet familiar enough with the two rhyolites, Leona and Northbrae, to tell them apart.

tunelroadchip.jpg

Roble Road debouches onto Tunnel Road very near the fault. If you head uphill on Tunnel, you cross the fault at the point in this photo. The house in the woods is at the corner of Vicente and Tunnel roads; its entrance has a stone block engraved “The Rocks.” Berkeley Rocks says that the house is perched on outcrops of the Leona Rhyolite. The wall in front divides the two opposite lanes of Tunnel Road. The chip on the right side, the only one on the whole wall, is probably due to movement on the Hayward fault.

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