At various times in a span of fifteen years, John McPhee made geological field surveys in the company of Eldridge Moores, a tectonicist at the University of California at Davis. The result of these trips is Assembling California, a cross-section in human and geologic time, from Donner Pass in the Sierra Nevada through the golden foothills of the Mother Lode and across the Great Central Valley to the wine country of the Coast Ranges, the rock of San Francisco, and the San Andreas family of faults. The two disparate time scales occasionally intersect-in the gold disruptions of the nineteenth century no less than in the earthquakes of the twentieth-and always with relevance to a newly understood geologic history in which half a dozen large and separate pieces of country are seen to have drifted in from far and near to coalesce as California. McPhee and Moores also journeyed to remote mountains of Arizona and to Cyprus and northern Greece, where rock of the deep-ocean floor has been transported into continental settings, as it has in California.
In his usual clean, graceful prose, McPhee takes readers on an intensive geological tour of California, from the Sierra Nevada through wine country to the San Andreas fault system, a 50-mile-wide swath of parallel fault lines. Through talks with his traveling companion, geologist Eldridge Moores, McPhee introduces the reader to current geological controversies, and surveys global plate tectonics--the collision and rearrangement of land masses ever since the breakup of the supercontinent of Pangaea eons ago. The duo also travel to Arizona, where Moores grew up pushing ore carts in his family's gold mine, and to Cyprus and Greece, where rock from the ocean floor has been tossed up to form continents. McPhee looks at the conjectural science of earthquake prediction and gives an account of a recent San Francisco quake. His leisurely excavation meanders from Mexican explorer Juan Bautista de Anza's settlement of San Francisco in 1776 to 1850s gold-mining camps to the summit of Mount Everest, made of marine limestone lifted from a shelf that once divided India and Tibet. With this volume McPhee concludes his Annals of the Former World series, which he began with Basin and Range (1980). Illustrated. (Feb.) -- PUBLISHERS WEEKLY.
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Farrar, Straus and Giroux
February 01, 1994
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Excerpt from Assembling California by John McPhee
You go down through the Ocean View district of San Francisco to the first freeway exit after Daly City, where you describe, in effect, a hairpin turn to head north past a McDonald's to a dead end in a local dump. It is called the Daly City Scavenger Company. You leave your car and walk north on a high contour some hundreds of yards through deep grasses until a path to your left takes you down a steep slope a quarter of a mile to the ocean. You double back along the water, south to Mussel Rock.
Mussel Rock is a horse. As any geologist will tell you, a horse is a displaced rock mass that has been caught between the walls of a fault. This one appeared to have got away. It seemed to have strained successfully to jump out of the continent. Or so I thought the first time I was there. It loomed in fog. Green seas slammed against it and turned white. It was not a small rock. It was like a three-story building, standing in the Pacific, with brown pelicans on the roof. You could walk out on a ledge and look up through the fog at the pelicans. When you looked around and faced inland, you saw that you were at the base of a fifty-foot cliff, its lithology shattered beyond identification. A huge crack split the cliff from top to bottom and ran on out through the ledge and under the waves. After a five-hundred-mile northwesterly drift through southern and central California, this was where the San Andreas Fault intersected the sea.
I went to Mussel Rock that foggy afternoon in 1978 with the geologist Kenneth Deffeyes. I have returned a number of times since, alone or in the company of others. With regard to the lithosphere, it's a good place to sit and watch the plates move. It is a moment in geography that does your thinking for you. The San Andreas Fault, of course, is not a single strand. It is something like a wire rope, as much as half a mile wide, each strand the signature of one or many earthquakes. Mussel Rock is near the outboard edge of the zone. You cannot really say that on one side of the big crack is the North American Plate and on the other side is the Pacific Plate, but it's tempting to do so. Almost automatically, you stand with one foot on each side and imagine your stride lengthening -- your right foot, say, riding backward toward Mexico, your left foot in motion toward Alaska. There's some truth in such a picture, but the actual plate boundary is not so sharply defined. Not only is the San Andreas of varying width in its complexity of strands, it is merely the senior fault in a large family of more or less parallel faults in an over-all swath at least fifty miles wide. Some of the faults are to the west and under the ocean; more are inland. Whether the plate boundary is five miles wide or fifty miles wide or extends all the way to central Utah is a matter that geologists currently debate. Nonetheless, there is granite under the sea off Mussel Rock that is evidently from the southern Sierra Nevada, has travelled three hundred miles along the San Andreas system, and continues to move northwest. As evidence of the motion of the plates, that granite will do.