View of “Mount Ararat”

One of the geologic puzzles I worked on during 2008 was the identity of “Rockridge Rock.” One candidate is a crag along Acacia Avenue once known as Cactus Rock; another candidate is an outcrop that supposedly was dynamited away in the early 1900s. I’m reluctant to accept either as the true Rockridge Rock without better evidence. In the meantime I’m intrigued by the hillock called “Mt Ararat” on an old map of the area. It’s topped with a bedrock eminence that’s almost completely hidden by homes and trees, but if you remove those (and there’s good historical reason to do that) I think what’s left is a legitimate candidate. This summer, while exploring the ground north of Mountain View Cemetery, I got a fair shot of the hill. Click the photo for a larger view.

I’ve been too busy to carry my search further lately, but I haven’t given up.

Oakmartre

I’ve kept this photo around for a long time, but I still can’t say exactly why. It reminds me of shots of Montmartre in Paris. It’s looking southeast toward the intersection of Park Boulevard and Chatham Road, which becomes a freeway onramp at this point. The road in the front is a nameless alley that branches off Excelsior Avenue, serving a tiny block of just nine houses.

I guess the shot exemplifies the hidden treasures of Oakland, hundreds of them, visible only to those who go about on foot with their eyes open. Not all of them are about geology. On top of the geologic palimpsest, the land bears another whole layer of human history: streets and lots laid out and partially erased leaving remnants and traces, not all of which can be deciphered. The people who witnessed the changes pass on, and details vanish. It is something like geology, whose story is likened to a newspaper with most of the pages torn out and the rest burned.

The Oakland geologic map

Time to share my geologic map of Oakland, adapted from USGS Miscellaneous Field Studies Map MF-2342. That map covers a much larger area, but I’ve cropped it to Oakland and faded out the neighboring cities. You’ll note the slash of the Hayward fault. Also note how much of the bay shore is fill. Click the photo to access the 2400×2400 version.

I know you’ll enjoy staring at this. To save traffic on my personal site, it would be best for youFeel free to copy the file to your own machine and view it at your leisure.

Happy holidays! By the way, I have a challenging Christmas geo-quiz up on About.com today; answers tomorrow in a separate post, so as not to spoil the experience for latecomers.

Rejuvenation

Big Daddy’s Complete Rejuvenating Community Garden sits astride the Emeryville line just north of 580 on Peralta Street at Macarthur. It’s a nice spot to look at the harmony between Oakland’s land and its history. There are the hills; here are the works of the city; beneath all is the same old soil, ready to bloom for us under the care and energy of visionaries.

Reclaiming dead land is the same work as reclaiming dead metal—making waste into wealth. There are many lessons and a lot of pleasure to be had at this urban garden. Click both photos for larger versions.

I probably will not blog here next week while the big annual meeting of the American Geophysical Union goes on across the bay. Look for activity on my About.com blog

Landslides

This fire trail in the hills is beginning to disappear downslope. The biggest mover of sediment is not erosion, it’s landslides—or mass wasting, to use the geologist’s more general term. The land is like a building in that respect: neither of them wear out, the way an ice cube melts; instead they get more and more rickety, then collapse.

This headscarp will concentrate the infiltration of rainwater at the same time it admits air underground. The comfortable stasis of the underground is now broken. The alternating wetting and drying and the rapid loading and unloading give gravity more advantages until one day it will pull the road down. Then the city will help mass wasting along by cutting a fresh track into the hillside. This will never end until the hill or humanity is gone. For us it’s just part of the cost of living.

Once you know these crescent scarps, you’ll see them everywhere in the hills.

Human geomorphology

This clandestine bicycle track in the woods overlooking Montclair seems to be abandoned; there are fallen trees lying across it. I’m assuming that it was used by pedal-pumping kids, because dirt bikes would have been heard for miles around.

It represents a huge amount of work. But that’s our specialty: digging up the ground for purposes far beyond our biological needs. Researchers calculate that human activity, from dam-building to mining and beyond, now surpasses every other single geologic agent in moving stuff around.