Archive for February, 2012

Clinton terrace

29 February 2012

Oakland has some small areas mapped as marine terraces. They run about 20 to 40 feet above sea level and they’re very flat. Here’s a look down 5th Avenue toward the bay that shows the terrace well, beyond the dip in the road. I was standing at E. 20th Street, on the Pleistocene fan; the low point in the road is at E. 18th Street.

clinton terrace

I name it Clinton terrace because it underlies the former town of Clinton. The terrace runs along the foot of the fan as far as Fruitvale. Here it is on the geologic map, unit Qmt, “Quaternary marine terrace deposits (Pleistocene).” I was standing at the asterisk.

clinton terrace map

In the map description, Russ Graymer correlates this terrace with other terraces along San Pablo Bay at Lone Tree Point and Wilson Point. Those have been dated at about 125,000 years old using uranium-thorium dating of oyster shells. That time was a well-known highstand of sea level, and coeval terraces occur up and down the Pacific coast. So we imagine the bay waves lapping against the older alluvial fan, nibbling off sediment and spreading it around to build a nice flat terrace. It was probably a lovely tidal marsh until the glaciers resumed, the sea fell and land vegetation moved in. Later, creeks dug into it along Park Boulevard, 14th Avenue and 23rd Avenue.

You can see there’s a bit more of the terrace under Lakeside Park. A final piece underlies the Valdez Street area beyond the upper left corner.

Gudde Ridge

19 February 2012

The basalt of the Moraga Formation is spectacularly exposed on both sides of Route 24 east of the Caldecott Tunnel. From along the highway you can get an excellent view of its makeup and structure, but this view from Radio Tower Hill shows how the rock unit makes up Gudde Ridge.

gudde ridge

Click the photo for the 1000-pixel verson. Gudde Ridge runs just east of Round Top all the way down to Canyon Road, on the back side of Moraga. The town of Canyon is on its west flank. And it’s Moraga basalt the whole way. In this photo you can see the underlying Orinda Formation to the right of the basalt. It’s gray conglomerate as opposed to the red-brown basalt.

Heritage in a dynamic place

10 February 2012

I gave my talk last night to the Oakland Heritage Alliance and I think it turned out well. I tried to talk about our geology not on its own terms, but weighted toward its relevance in Oakland’s general civic life. One of my slides was this lovely digital elevation model that makes the Hayward fault obvious. Click to see the whole thing. Sadly, I can’t recall exactly where I got it.

oakland DEM

Here are my concluding remarks from the talk.

Oakland is situated in an area that falls down every century or so. Today, a repeat of the 1868 earthquake would erase large areas of our city. I don’t see how we can prevent that. How can we hang on to our history in the face of nature? And how can we hang on to our history in the face of human nature? By that I refer to well-known tendencies in cities that are traumatized. Citizens have a strong, almost overwhelming urge to return to normal, and that drive is amplified in their leaders.

We have the example of San Francisco after 1906, which underwent a furious rebuilding and whose leaders had no tolerance for delay. San Francisco was the leading city of the West, and the stakes were very high. Democracy was short-circuited for a time. The development-driven city leaders, led by “mover and shaker” James Phelan, were prepared to obliterate Chinatown before the Asian-American community rallied to save it. There was no heritage community at the time, and who knows how it would have fared had there been one.

After our earthquake—and it’s coming—Oakland will still have all the geographical gifts that I showed you at the start of my talk. We can assume that the seaport and airport and rail lines and highways will be rebuilt as soon as possible. The stakes will again be very high. There will be little conflict with the heritage community over any of that. The hard part will begin once the emergency ends.

Earthquakes are part of our geography. These days we like to talk about sustainable living: in tornado country, for instance, that means everyone has a storm cellar. What does it mean in Oakland? Some of our most beautiful neighborhoods lie along the fault, and they probably will not be reoccupied once destroyed. The city that arises after the next Big One will be very different in some ways.

I think I can foresee a more sustainable Oakland in which more people will live in well designed multi-family buildings and recreate in a long greenbelt where route 13 runs today. On the other hand, much will endure. City Hall should survive thanks to its retrofit after 1989. Landmarks like Tech High, the Camron-Stanford House, Peralta Hacienda, and Dunsmuir will be restored if they survive the tumult. I know that the Oakland Heritage Alliance will be there, doing its utmost to save what can be saved. In the end, much depends on the citizenry at large: the values they hold most strongly, the values we are teaching them today, will be those that prevail.

Home from afar

5 February 2012

A few weeks ago I paid a visit to distant Mount Vaca, north of Fairfield on the Solano-Napa County line. It’s almost 3000 feet up and commands a wide view. Naturally I looked back at the Oakland Hills. There they were, immediately recognizable.

view from Blue Ridge

Click the photo for a 950-pixel version. In the upper center is Round Top, with Redwood Peak to the left and Vollmer, then Grizzly Peak to the right. Behind them is San Bruno Mountain across the bay. On the left edge are the plumes from the Avon refinery near Martinez and a bit of the Delta. The entire vista is part of the plate boundary, cut into slivers by the strands of the San Andreas fault system. At geological speed, they are all moving rightward at various rates measured in millimeters per year.

I’m working on my talk for the Oakland Heritage Alliance, this Thursday at 7:00. The process is forcing me back away from the details and toward the big picture—not the geological big picture, but the picture nongeologists see. That means I talk less about plate boundaries and more about how to live on our particular one.


Follow

Get every new post delivered to your Inbox.

Join 4,040 other followers