In the old days of college science reqs—before the 1960s—economics was still the dismal science, and geology the dull one. Then plate tectonics began shifting the lay of the land. Geology got sexy. The New Yorker got a geology beat.

John McPhee spent fifteen years on it, mostly in the company of the hot new geologists called plate tectonicists, scientists who had to invent so many geoneologisms that McPhee called them “geonovelists.” McPhee himself stockpiled “palinspastic reconstructions,” “pulsating glaciers,” “discordant batholiths,” and “incompetent rock.” He wrote a tectonics tetralogy, saving “the far-out stuff … in the Far West,” “a leather-jacket geology in mirrored shades,” for last. Published a year ago, Assembling California is a seismic take on the “extensional disassembling of the earth” going on there.

Now into this same far-out country comes Kenneth Brown, in the company of “mobility-minded geologists” (too many interchangeable talking rock heads), also to address the “well-tuned machine” of plate tectonics on the North American continent’s cutting—Pacific—edge. In P.T., “continents were suddenly mobile and shifty things. They jumped about and wandered across the face of the earth . . . [which] was not uniform and unchangeable but divided into plates of oceanic and continental crust.” For two years, Mr. Brown scouted the six-thousand-mile route that the “mobile Pacific Plate” will travel over the next two hundred million years while “speeding toward Alaska at the rate of some two inches per year.” Alaska is the destination of Los Angeles, Santa Barbara, San