Archive for November, 2008

Thanks, Oakland

27 November 2008

oakland panorama

On a gorgeous day two years ago (it was 11/29) I made a field trip to Corona Heights, across the bay in that other city, and shot this view of my home town. Soon I turned it into the banner image for this blog. I thought I’d offer a larger version—just click the photo for the 1600×835 size. It doesn’t get the whole city, only from Hiller Highlands down to Crestmont, but it gets the essence: green hills, wide lowlands, a handsome downtown, a busy harbor.

San Francisco is a fine place (it certainly has us beat for slickensides), but Oakland is where I’ve been happy to live for almost 20 years. I feel like I’m just getting to know it.


Thrust and fold

21 November 2008

The same day I was up at Redwood looking for the bent trees, I ran across this fine example of a thrust fault right next to the Huckleberry Botanic Reserve.


Today I finally got around to putting it in my gallery at—not as a thrust fault (I already have a good one), but as an example of a drag fold. Looks pretty good there, almost textbook quality. But here’s a secret: look at this view of the fault.


I can’t figure out what the double curvature means! I can’t figure out the relationship of the fault to the folds. I feel like a freshman in his first field course. A real geologist would crawl all over this, including the hillside on top, until everything was clear. But I tell myself, the key to being a good scientist is to admit when you’re mystified because enlightenment comes that way. A certain set of people can visualize things ten times as complicated, and I hope one of them will pipe up.

By the way, my spread about Oakland’s geology is in the new Oakbook, the printed one. Go get one for free.


17 November 2008


Here is a nice example from the Oakland hills of breccia, a kind of rock that consists of broken pieces of rock. There are several different ways to make a breccia, and not having a lab and a petrographic microscope I can’t specify what made this. But considering that the hills have been raised by vigorous tectonic action accompanied by earthquakes, it’s easy to imagine some seismic event opening a fracture, shattering the rock, and allowing mineral-charged fluids into the space. Other ways involve dissolving the rock until it collapses, slumping while the rock is young and poorly consolidated, and simply cementing together a pile of landslide debris or volcanic deposits.

Because breccia really signifies an activity rather than a material, geologists would rather think about brecciation when they see a breccia.

UPDATE: I should mention that I have lots more breccia pictures on start here and try a search on “breccia” for more.