Thumbs tucked, fingers flat, the hands side by side, she presses them hard together until they buckle upward. The hands are two continents, or other landmasses, converging, colliding-making mountains. The Himalaya was made that way. Placing the hands flat again, she slowly moves them apart. These are two plates separating, one on either side of a spreading center. The Atlantic Ocean was made that way. She begins to slide one hand under the other. This is subduction. Ocean floors are consumed that way. Thumbs tucked, fingers flat, palms again side by side, she slides one hand forward, one back, the index fingers rubbing. This is the motion of a transform fault, a strike-slip fault-the San Andreas Fault. Parts of California have slid into present place that way. Convergent margins, divergent margins, transform faults: she has outlined the boundaries of the earth’s plates. There is enough complexity in tectonics to lithify the nimblest mind, but the basic model is that simple. Take your zakelijke energie vergelijken hands with you-she smiles -and you are ready for the mountains. When I first went into the Sierra with Judy’s husband, in i978, he had an oyster-gray Volkswagen bus with a sticker on its bumper that said “Stop Continental Drift.” I guess he thought that was funny. There were not a few geologists then who really would have stopped it in its tracks if they could have figured out a mechanism for doing so, but, since no one knew then (or knows for certain now) what drives the plates, no one knew how to stop them. Plate tectonics had arrived in geology just about when Moores did, and-in his metaphor-he hit the beach in the second wave. He has called it “the realization wave”: when geologists zakelijke energie began to see the full dimensions and implications of the new theory, and the research possibilities it afforded-a scientific revolution literally on a global scale. Physiographic California, for much of its length, is divided into three parts. Where Interstate 80 crosses them, from Reno to San Francisco, they make a profile that is acutely defined: the Sierra Nevada, highest mountain range in the Lower Forty-eight; the Great Central Valley, essentially at sea level and very much flatter than Iowa or Kansas; and the Coast Ranges, a marine medley, still ascending from the adjacent sea.