Longtime commenter artisancrafts reminded me, in a comment to my last post, that there’s a nice exposure of blueschist at the north edge of Mills College. Yesterday I easily located it by following his/her directions. First there’s the old railbed that once ran to Laundry Canyon. This stretch of it, which once continued down through the Fan parallel to High Street, used to be part of Courtland Street.
At the spot in the distance where the sun shines across the roadbed is this lovely exposure, about 2 by 3 meters.
It’s clearly worn by water, and a little concrete-lined ditch running along the uphill side of the roadbed feeds it. Following it upstream takes you right up to the 580 freeway abutment, where it veers north in a culvert. The stream is a mystery that I won’t try to solve today.
Back to the rock. Getting closer to it, you may not believe your camera. Clear blue skylight can do that.
This closeup, showing tightly folded lamination in the cleft on the right edge of the first shot, is a truer indication of its color thanks to my camera’s flash.
It’s classic blueschist, the largest outcrop of it I’ve seen in Oakland. Let’s call it blueschist-grade melange, what’s usually referred to in Franciscan circles as a high-grade block, and I’m very pleased to know that we have one in town.