Next morning, with that warm early light and a thin fog in live oaks dripping with moss, we entered an 80-mile stretch of the fault known in geology as the Central Creeping Zone. Here in Cholame, where James Dean died in a car crash, it was as if we'd passed from Nevada into Maryland. The earth was a rich chocolate brown, and the farms were the wealthiest we'd seen, classic red barns and white picket fences at the edges of sag ponds.

As you drive north from Pinnacles, the landscape becomes increasingly agrarian. Vineyards start to dominate, spreading out row upon row in soothing repetition. On Cienega Road is a former Almaden winery. It lies beneath Atlas cedars and one lone palm tree. Now the property is owned by Aqua Futures, and old oak casks strewn about the parking lot are the only indication that wine was produced here. Though its buildings straddle the San Andreas Fault, it closed down after a little-known fault, the Quien Sabe, sprang to life in 1986. The epicenter was 25 miles away. Even so, the shaking caused a 20,000-gallon vat of cabernet sauvignon to break open and spill out into the road. The moral: Who knows.

And who knew? In 1797, long before plate tectonics, Father Lasuen founded the Spanish mission of San Juan Bautista not far from the former winery. Scouts had discovered wells at the site, and soon thereafter building began. The mission stands on the edge of a 50-foot escarpment raised by—and right on—the San Andreas Fault. Repeated earthquakes in 1800 demolished part of the mission. The earth shook, but it did not shake the faith of the good fathers. They kept strengthening the structures, as later Californians have been forced to do. The mission was dedicated in 1812.

The building, with its pale adobe walls, porticos, and red-tiled roofs, is a quintessential California mission. From its perch on the scarp, it overlooks the wide and fertile Llano del Tequisquite, from which the Santa Cruz Mountains seem to rise. So lovely and mysterious is the setting that Alfred Hitchcock used it as the mission in Vertigo.

We visited San Juan Bautista on Christmas morning, a clear and warm day, the plain so alive with its rich dark fields it seemed anything could grow there. A Mass was in progress, and the congregation sang Christmas hymns as we wandered around the grounds. We were most interested in the scarp. Now covered in thickets below the mission, it had once been a grandstand for dog races and rodeos in an arena spread beneath it on the fault trace. I imagined the monks more than 200 years ago, looking out over the Llano del Tequisquite and the Santa Cruz Mountains for the first time. Despite the fault and ignoring a few telephone poles, the scene had probably not changed much.

The monks didn't know they were building on the fault, but today if you build on it you know. In Los Gatos, which is about 50 miles north of San Juan Bautista, my uncle Alan and aunt Jenny live in a sprawling ranch house in a deep ravine of redwoods and madrones directly on the fault. We spent the night in a guest bedroom with picture windows overlooking the fault. At dusk, all five of us relaxed in a Jacuzzi on a vast redwood deck cantilevered over the fault. In the 1989 earthquake, this house shimmied itself across its own foundation like butter in a hot skillet.