Serpentine at Coolidge hook

At the top of Coolidge Avenue, the road hooks sharply to the left just below the grounds of the LDS Temple. Right there is a nice exposure of serpentine rock.


Its green color and scaly appearance are obvious and unlike the brown sedimentary rocks downhill from here. Serpentinite is not mapped here, so make of that what you will. I tend to assume that serpentinite is likely anywhere along the Hayward fault (which is a about a hundred meters uphill from here, running through the temple parking lot). Take a closer look at the rounded blocks amid the scaly matrix.


This is the block at upper right in the photo above. It gets its rounded look from being rotated and scrubbed during lateral shear, like a lump of cold butter in piecrust. Here’s the block to its left.


The block’s surface is festooned with slickensides:


And the sheared matrix is also well exposed on its upper side.


The views in the other direction are great, too. This is pretty much the view you get from the temple grounds, and unlike the temple it’s always open to the public.

2 Responses to “Serpentine at Coolidge hook”

  1. artisancrafts Says:

    Looking over that area via old topos and prewar? aerial photos, you can see that area being excavated extensively. Could the serpentine may have been relocated to that spot from somewhere higher up?
    Also, the earthworks could have exposed it? How and when do these geological map surveys take place?
    That’s such an interesting area.

  2. Pete Veilleux Says:

    i can recognize a place w/ serpentine bedrock immediately – just by seeing what grows there. whether it’s native or invasive, there are certain associates which are unmistakable. have you checked out the serpentine on Crestmont? years ago – when the development surrounding it was under construction – a friend and i found loads of very rare plants – Tiburon Buckwheat, Presidio Clarkia, Most Beautiful Jewelflower – all listed endangered species were found all over the site – and for some, in the largest populations ever found. we were able to put the breaks on the construction but for about one year. we looked up the epr’s to see what they said about the development’s affect on local ecosystems would be. their report on the vegetation was simply – ‘all invasives. nothing native.’ this illustrates well how little teeth our environmental protection agency really has in order to enforce environmental law.

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