On the Rocks : ASSEMBLING CALIFORNIA By John McPhee , (Farrar, Straus and Giroux: $20; 264 pp.)

Before the theory of plate tectonics--that is to say, before about 1968--those of us who went to college with underdeveloped right brains frequently fulfilled the university science requirement by suffering through two semesters of geology, a subject we incorrectly imagined might prove more comprehensible than physics or chemistry or statistics. All I retain from that experience is the misinformation (now dismissed as “the old geology”) that mountains were formed when the skin of the earth shriveled up; sediments eroded into troughs called geosynclines at the foot of the mountains, and the accumulating weight eventually put such pressure on the Earth’s mantle that it rebounded isostatically, pushing the mountains higher. Or something like that. Even though it turns out this isn’t true, I got a D in the course and fled happily back to the humanities.

Had John McPhee written his tetralogy, “Annals of the Former World,” of which “Assembling California” is the final volume, I might have had a very different attitude toward the structural history of the Earth, not to mention a better understanding of it, for McPhee has the ability to disarm an averse student with deft analogies, sprightly metaphors, the gentle grace of amusing anecdotes--in short, with the sheer power of his narrative skills. Here is a meager sampling:

“At work or play, a geologist always drives like Egyptian painting--eyes to the side. . . .

“The south-flowing river is . . . dammed to reserve the snowmelt of the Sierra Nevada, not only to flood the rice fields and irrigate the other crops of the valley but also to travel six hundred miles in a life-support tube that is taped to the nose of Los Angeles. . . .

“The Hayward Fault runs not only through Memorial Stadium but also through or very near the Alameda County hospital, the San Leandro hospital, and California State University, Hayward. The Hayward Fault also ran through the California School for the Deaf and Blind, but the State became nervous, moved the school to another site, and then filled up its old dorms with Berkeley undergraduates.”

Moreover, McPhee casts himself in the role of student as he follows Eldridge Moores, a tectonicist from the University of California at Davis, over hill and dale, observing, listening, asking questions, trying like the rest of us to understand the puzzling evolution of continental formations and deformations. It is a narrative stance, however disingenuous, that helps inveigle us into believing that the abstruse may become, if we hang in there, comprehensible.

Like the other three books in the tetralogy (“Basin and Range,” “In Suspect Terrain” and “Rising From the Plains”), “Assembling California” is in no small part a strapping explication of the cause and effect of plate tectonics, albeit written mostly in a language that even a D student can understand. Still, there is plenty of tough sledding and not all readers are going to have the will to slog through miles of sentences like “The chamber, in cooling, tends to form strata . . . but above these cumulative bands it becomes essentially a massive gabbro shading upward into plagiogranite as the magmatic juices chemically differentiate themselves in ways that relate to temperature.”

The theory of plate tectonics has it that the rind of the earth is made up of lithospheric plates, plates of crystal and mantle rock that descend to a depth in the earth where rock becomes lubricious and “floats” on the molten core. Most of these lithospheres are in constant motion. When they converge and crash into one another they buckle upward--making mountains. When one dives under the other (known as subduction), the over-thrusting lithosphere tilts upward, making mountains. When they drift apart and separate, they create oceans in their spreading center. And when they collide and slide past one another, in a motion called transform or strike-slip faulting (as in the San Andreas fault), they cause residents along the margin of the Pacific and North American plates to consider the wisdom of their chosen habitat. McPhee assures us, “There is enough complexity in tectonics to lithify the nimblest mind, but the basic model is that simple.”

So what do the 158,693 square miles of California have to do with all of this? Set aside your fear and loathing of scientific jargon (there’s plenty here that is not) and read McPhee’s book. “Assembling California” is the geological history of that physiographic congeries whose regional parts we all think of as the Sierra Nevada, the Modoc Plateau, the Klamath, Cascade, Coast and Peninsular Ranges, the Great Central Valley. Until very recent geological time none of this existed. California was not here. Nowhere, not even lurking underwater waiting to emerge. The land mass of North America ended far to the east of its current boundary and beach-front property lay somewhere in the vicinity of Nevada, or Utah.

“Then,” as McPhee tells us, “a piece at a time--according to present theory--parts began to assemble. An island arc here, a piece of a continent there--a Japan at a time, a New Zealand, a Madagascar--came crunching in upon the continent and have thus far adhered. Baja is about to detach. A great deal more may go with it. Some parts of California arrived head on, and others came sliding in on transform faults, in the manner of that Sierra granite west of the San Andreas.”

As it turns out, the assembling of California is more than a comprehensible story, it is a fascinating drama. OK, the reader may wish to know a bit less about gabbros, pillow basalts and plagiogranites than McPhee tells him, may even wish that McPhee and Moores were more flamboyant characters in the narrative, like Brower and Dominy in “Encounters with the Archdruid” or Ashe and Bradley in “Levels of the Game.” But this is a biography of the earth (as we understand it today). It has its own schizo personality, and is flamboyant enough on its own, as any survivor of the Loma Prieta earthquake will testify. It’s well worth getting to know a little better.