The fire zone

I was across the bay on October 19, 1991, doing a freelance job at some client whose name I forget. It was a hot day, and I saw a tall plume of smoke in the Oakland hills. The fire people worked on it, and that evening as I headed back across the bay it seemed to be over. But the following day, 20 years ago today, an ember got loose and took out a huge swath of the hills with some three thousand homes on it. It was a terrifying day, like something out of Lord of the Rings. Thick smoke covered the whole sky, and the east wind wouldn’t let up. The city was at nature’s mercy until the winds turned, late in the afternoon. For years afterward we would find pieces of charred wood in our garden that had dropped from the sky that day.

Apparently the same thing had happened in 1970. Historians reminded us that it happened in 1923, too. Before that the native inhabitants made a practice of torching the hills often to keep the land clear. But in the aftermath of 1991 the hills were hastily repopulated and reforested by residents whose driving urge was to make the pain stop. They had the eager help of insurance companies, placing their bets on the enduring value of view lots.

Today these fireprone hills are platted out for houses forever, even the impossible slopes of Charing Cross Road. Now the hills are in an unsustainable cycle of building expensive homes cheek by jowl on inadequate streets, growing inertia as fuel builds up and preparations lapse, one dire day of conflagration, and heedless rebuilding. The earthquake cycle is just a slower version of this fire cycle. If madness is doing the same things in the face of futility, then Oakland has gone mad. It doesn’t have to be this way.

Sidewalk weathering

I look at sidewalks more closely than most people. It has little to do with geology, though—it’s just part of my hobby. But sidewalks do have geological lessons in them. Consider this sidewalk on the north side of upper Broadway near Lake Temescal.

It has a series of light-colored wedges along the fence, on the uphill side. As you might guess, they reflect the pattern of the rainfall and its drainage. Fresh concrete is poured and then caressed with trowels as it begins to cure. This treatment pushes the larger particles of aggregate under the surface and creates a smooth finished surface composed of fine particles and cement. But the surface tends to weather off, partly because the surface is hard to keep moist for proper curing. The imperfectly cured material is prone to attack by rainwater, which is a mild acid. As rain and wind work into the surface, green things both microscopic and visible colonize the rough spots. These turn up the acid attack with exceptionally high CO₂ levels similar to those in soils, along with humic acids produced by plant tissues. With time, the crisp white walkway turns rough, variegated—and beautiful, akin to natural stone.

Upper Claremont Canyon

I’ve been busy, and October is the climax of the business. But I have a fond memory of May 26, when I hiked up to and past the end of Panoramic Way into the open lands of the Claremont Canyon Regional Preserve. The ground here is mapped as undifferentiated sedimentary rocks of the Great Valley Complex. Because the map doesn’t give it a name, I name it Panoramic ridge. This is the view east. Click the photo for a 1000-pixel version.

I wonder about the pattern of the ridges that jut west from the ridgeline, but that’s an intellectual task for another time. For now my main thought is, We live in such a beautiful area.

I’ll be out of town for much of the month, so don’t expect a lot of new posts for a while.