"You see the whole human story written in this valley," my father said from the backseat. "The San Andreas Fault is functioning on such a different time scale, so very different from the human scale, that humans have developed a talent for ignoring it. Since Columbus landed, this stuff has moved only a few feet. When you say the fault might move in a major way once every few hundred years, you can certainly understand why human beings are indifferent. But on the other hand, if you're here on April 23 in the year 2920 and that happens to be the day when the human scale and the geological scale intersect—boom, you're in an earthquake. In the meantime, you have this peaceful, beautiful country. What are you going to say to somebody about putting his ranch here and raising his kids? Maybe he feels only the slightest tremor, but later on his great- grandson is deader than a duck." Signs on the road registered concern on the human scale: "Earthworm growers wanted." "Jesus is the reason for the season." Since Jesus' birth, Salinia has moved only about 400 feet.

We descended to the Carrizo Plain in the morning on the Cerro Noroeste highway, a ridge road with stunning views to the east into the San Emigdio Mountains in the Coast Ranges, out across the Great Central Valley to the snowcapped peaks of Mount Whitney and the Sierra Nevada, and straight ahead into the flat expanse of the Carrizo Plain. On the Cerro Noroeste, you are in big country with an immaculate silence. Though the mountains have been warped into shape by the fault, the fault is lost, to our view, within them. Picnic spots and campgrounds are tucked in canyons, and I could imagine taking this drive, camping and picnicking, in the spring with the wildflowers. Now there were patches of snow and ice, and a gentle mist lay over everything beneath us like a veil.

In the Carrizo Plain I first read the land. The lack of vegetation makes it easier to see the scars. Offset streams and scarps and linear ridges are there for the viewing. Creeks running down Elkhorn Scarp were offset by the Fort Tejon earthquake, and we hunted for them—for one in particular, named Wallace Creek. Spotting it sent a rush through me. Here, what had seemed subtle before was not subtle at all. The stream had literally been sliced in two and moved. In one jump, the bottom half of the creek had shifted almost 30 feet closer to Alaska. We hiked up to the shear zone and walked on the evidence of two plates, 6,000 to 8,000 miles wide, sideswiping each other. Dozens of blue birds flew about, and the moon shone brilliantly in the pale sky.

In geologic terms, the Carrizo Plain appears to be a pull-apart basin. As the two plates slip past each other, every once in a while they hit a snag of some sort (a "releasing bend") that causes them to pull away from each other and open into a trapezoid. If the rock is soft, the valley that forms in the trapezoid will soon be deeper than a valley made by water. Sag ponds are minor versions of pull-apart basins. The Napa Valley is a pull-apart basin. Standing in Yountville, in the gut of a pull-apart basin overlooking Soda Lake frothing white with saline water, I found it hard to imagine that a few days later we'd be at the French Laundry, sipping French Champagne and gorging on a 12-course tasting menu: beluga caviar with Yukon gold potato blinis, scrambled farm-fresh eggs with white truffles from Alba, sautéed Moulard duck foie gras.