Annals of the Former World

by John McPhee

  Moores remarked, “If you want to find a fault in California, look for a dam.”

  Scarcely had the dental work been completed when, in 1975, an earthquake struck near Oroville, forty-five miles up the Smartville Block. Its Richter magnitude was 5.7. Near Oroville on the Feather River was the eighth-largest dam in the world. It had been completed in 1968, only seven years before the earthquake, and gradually its reservoir had impounded forty-six hundred million tons of water, or enough to put a lot of pressure on the rocks below. It was a gravity dam, broad and squat, an earth-fill dam, and what it had been filled with was seventy-eight million cubic yards of hydraulicgold-mine tailings. Absorbing the earthquake, the dam just sat there, holding its lake. However, the United States Geological Survey (a sibling agency of Reclamation within the Department of the Interior) quietly noted that twenty-five per cent of reservoirs of comparable depth had, by their sheer weight, triggered earthquakes. The earthquake at Oroville had been five times larger than the maximum earthquake that the dam at Auburn was designed to withstand.

  This collection of facts soon assembled itself in the editorial offices of the Sacramento Bee. On its front page the Bee envisioned an earthquake that would knock out Auburn Dam, releasing water that would in less than two hours stand in Sacramento twenty feet deep. In the words of a former Assistant Secretary of the Interior, this would be “the worst peacetime disaster in American history.” Estimates were that a quarter of a million people would drown.

  The federal government considers faults inactive if they haven’t jumped for a hundred thousand years. The latest known movement along the F-1 Fault in Auburn was in the Jurassic—a hundred and forty million years before the present—but that did not soothe Sacramento. Work on Auburn Dam was suspended. In 1978, Moores and I found the site silent, dry, reliquary. It looked that way many years later, when we went there again. Geologic time and human time seemed to have met and parted.

  Mountain lions go through the dam site. Bears. Feral goats. The project is dormant and appears dead, or vice versa, depending on how the beholder eyes it. The bureau keeps a skeleton crew there, each of whom speaks of the dam in the future positive.

  You ask at what altitude the lake level was to be.

  Response: “The lake level will be eleven hundred and thirty feet.”

  You ask if the boat ramp would have been paved.

  Response: “Yes, that will be paved.”

  The gravel boat ramp, several hundred yards long, descends a steep slope and ends high and nowhere, a dangling cul-de-sac. The skeletons call it “the largest and highest unused boat ramp in California.” Houses that cling to the canyon sides look into the empty pit. They were built around the future lakeshore under the promise of rising water. You can almost see their boat docks projecting into the air. Thirty-three hundred quarter-acre lots were platted in a subdivision called Auburn Lake Trails.

  Moores wanted to know if a geology student from Davis might be permitted to study the rocks that had been exposed during construction.

  “Fine, but we would not want the student’s conclusions to inconvenience the dam.”

  The dam has cost several hundred million dollars so far. The bureau spends a million dollars a year maintaining the site while nothing happens.

  We looked for a cup of coffee in Cool, California, after crossing the American River on a seven-hundred-foot-high bridge. Not particularly long, the bridge was built so high in order to clear the lake that wasn’t there. From houses in Cool, picture windows framed the lake air. There were numerous for-sale signs. Mother Lode Realty. Cool was a placer-mining camp of the eighteen-fifties. In Cool Quarry, marine limestone is mined now—a lenticular pod, a third of a cubic mile, shoved into California by the arriving Smartville Block. If you had lived on the moon then, as a full earth came into the sky you would have seen two large continents (Laurasia and Gondwanaland), one above the other, surrounded and divided by ocean. West to east, the dividing seas were the incipient Caribbean (Central America was not there), the incipient Atlantic, and—from Gibraltar through China—the long water known in geology as Tethys. Worldwide, fossils from that time are described as Tethyan. Tethys, mother of rivers, was the consort of Oceanus. Cool was named for Aaron Cool. In the limestone pod in Cool, California, caught up in the docking of the Smartville Block, are Tethyan fusilinids and Tethyan corals.

  As an overriding plate scrapes the plate below, it acts like the blade of a bulldozer and piles up sand, seashells, cherts, phyllites—whatever happens to be there. Impressive amounts of material can be accreted in this manner. As the Philippine Plate has scraped westward, overlapping the Eurasian Plate, an accretionary wedge has risen as Taiwan. In an arc-to-continent collision that is reducing the distance between Taipei and Beijing, Taiwan is the first piece of the West Luzon Island Arc to reach the Eurasian slope. In the melange of rocks in the Taiwan accretionary wedge are not only sands, seashells, cherts, and phyllites but enough scraped-up ocean-floor debris—sheeted dikes, pillow lavas, gabbros, serpentines—to be known as the East Taiwan Ophiolite. A large and intact package of ocean crust-and-mantle can be expected to follow, as one did when Smartville began to close with North America.

  The Smartville Block pushed before it not only the limestone of Cool and the schists and serpentines of Auburn Dam but also the red-weathered phyllites and the argillites and cherts we had seen along the interstate as we descended toward Auburn. These and a great miscellany of additional rocks were Smartville’s melange, its accretionary prism—highly foliated, sheared, broken, disrupted, deformed—caught up in the Smartville suture, the docking of arc and continent.

  There was, of course, a subduction zone—a trench—between the arc and the continent as they drew together, and in the collision it disappeared. It was actually stuffed shut, according to present theory. First, ocean crust-and-mantle of the North American Plate went down the trench. Eventually, the continental rock itself reached the trench and jammed it, like a bagel in a toaster. Continents are too light and thick to be subducted, and where they arrive at trenches the trenches cease to function. Australia has jammed the trench to the north of it with such force that it has produced New Guinea. As Moores envisions the Jurassic event in California, a large overlap of Smartville ocean crust (the upper plate) was left lying on the North American continental slope after subduction stopped. The region cooled in the postcollisional stillness. The lower, west-moving plate was no longer descending, dragging everything downward. Isostasy, the force that lifts light objects when other forces cease to hold them down, began to work on the combined terranes. Lifting them, it broke off a large piece of the Smartville ocean crust-and-mantle and carried it into the air in what would eventually become the foothills of the Sierra Nevada.

  As a geological and geophysical specialty, the study of ophiolites is only a few years old, and therefore provokes argument on almost any question raised—from the environment of the origin of the rock itself to the putative method by which it made its way from extracontinental depths to dry land. The emplacement story for the Smartville Block was worked out by Eldridge Moores.

  Descending westward, just below Auburn, you cross the thousand-foot contour, and the Great Central Valley comes into view, running flat out of sight to the horizon. Sacramento is down there, and, fifteen miles farther, Davis. It is an abrupt, absolute change of physiographic worlds, where the mountains hinge. The Smartville Block extends under the valley and ends beneath the Coast Ranges.

  After the trench at Auburn disappeared, another one had to develop, as the trailing edge of Smartville became the new front of the North American Plate, moving west. To balance the earth’s books by consuming an amount of ocean crust comparable to what is made at spreading centers, subduction zones develop when and where they are needed. Across geologic time, subduction zones have come and gone quite often. On one side of the Smartville Block the new subduction must have been developing even while the old subduction died on the other. “For sure,” Moores said. “You�
��ve got to produce that convergence somewhere. You don’t cut things off. The subduction here at Auburn was Permian to early Jurassic. The new subduction zone to the west was operating by the late Jurassic, and it operated all through Cretaceous and into Tertiary time. The volcanoes came up in the Sierra, and the main batholith formed. I think the geology is really neat. The new plate margins produced their own accretionary prism, piling up out there to the west of us to become the rest of California.”

  Moores had become aware of the unusual rocks in the Sierra foothills only four years before I met him. On a spring day in 1974, he and his family left Davis for a camping trip in the mountains, and instead of following their usual route, up the Feather River, they took a right at Yuba City and went into the canyon of the Yuba. The theory of plate tectonics was six years old. Eight more years would pass before the term “exotic terrane” would be coined. Geologists, caught up in the fresh intensity of a scientific revolution, were still at the beginnings of seeing the world anew. Few people then envisioned the western United States as a collection of lithospheric driftwood. Moores, however, had worked for some years in Macedonia, struggling to understand the large unrooted masses of mantle rock that lay there on the surface as mountains, and to relate it to the stratiform gabbros, plagiogranites, and sheeted dikes nearby. With Fred Vine, now of the University of East Anglia, he had also worked in the Troodos Mountains of Cyprus, where sheeted diabase ran on for seventy miles, and where the gabbros, the granites, and capping marine sediments were present as well. Moores and Vine decided that the whole assemblage had somehow been removed from a blueocean setting and emplaced upon the African slope. In 1971, they published in the Philosophical Transactions of the Royal Society (London) an establishing paper, the significance of which was expressed in its title: “The Troodos Massif, Cyprus, and Other Ophiolites as Oceanic Crust.”

  Between the Great Valley and the High Sierra, the Yuba drainage lay in the geographic center of what was not yet known as the Smartville Block. Moores wasn’t there to do geology. All he was trying to do was to go uphill out of the oak woodland and into the ponderosas, a task to which his micropowered microbus was almost unequal. It chugged, and—among the brown grasses of a dry country—the rock at the roadside passed slowly. At work or play, a geologist always drives like Egyptian painting—eyes to the side. Near the tributary Dry Creek, about ten miles north of the Yuba, the microbus ascended a particularly formidable incline between high roadcut walls of a dark and igneous rock. Moores did not stop, but the hair on his arm may have moved. He remembers feeling that he could have been in Macedonia. More emphatically, in Cyprus.

  On the geologic map of California, the lithology of that area was vaguely described as “Jura-Triassic metavolcanic rocks.” The eye sees what it is trained to see. Or, according to a maxim that Moores often quotes, “the eye seldom sees what the mind does not anticipate.” When Moores returned to that roadcut with a lens in his hand, he did not need it. He found—one standing beside the next beside the next beside the next—classic sheets of sparkling diabase, each with a glassy margin, all in prime condition, undeformed.

  The sheeted dikes that he would later find on Interstate 80 at Auburn were deformed in the Smartville suture almost beyond recognition. These in the Yuba Valley were well back of Smartville’s impacted leading edge. When he and I stopped there once, he said, “You could look at hand specimens of rocks taken from this cut and not be able to say if they were from Cyprus, Pakistan, Oman, New Guinea, Newfoundland, or California. Only by dating and by detailed chemical analysis of minor elements can you tell them apart.” From Auburn Dam north to Oroville, there is a continual exposure of forty miles of these sequential laminations of seafloor spreading.

  I asked him if he could say from what distance and what western compass point the Smartville Block had come.

  “No,” he said. “We have tried doing paleomagnetic work, but so far it’s inconclusive. The Smartville arc probably developed not more than a thousand kilometres from North America. It probably came from the northwest.”

  In altitude, the Smartville Block rises roughly from zero to five thousand feet. To move about on its small roads is to move among zones of time that are not all written in rock. U-2s drop out of the stratosphere and hang-glide into Beale Air Force Base while you walk up a dry streambed at Oregon House, where placers were first panned in 1850, in a valley of sheeted diabase that was injected into the floor of the North Pacific Ocean about a hundred and sixty million years ago and emplaced on California five million years after that. The ophiolite—the whole vast assemblage of transported deepocean rock—now rests on California like a ship stuck in sand, listing thirty degrees to the west. The ophiolite tilts more steeply than the slope of the Sierra. Therefore, as you climb the modern foothills, geologically you go downsection, ever deeper into the former seafloor, from the spreading rift to the granites and gabbros of the magma chamber that fed it, and on to the cumulate layers of heavy crystals that settled on the mantle at the boundary that is known in the science as the Moho. On up the mountains (and farther downsection) are scattered serpentines derived from the mantle itself. Where the rock has not been folded, the descent of the ophiolite is as clear as it is complete. It is the perverseness not of the science but of the earth itself that you often go downsection when you are going uphill.

  In the other direction, the ocean-crustal rock that lay above the sheeted dikes is in the foothills also. Below Timbuctoo Bend on the Yuba, for example, a green ledge of what appear to be massed satin pillows reaches into the fast clear river. Notwithstanding the boulder fields of hydraulic-mining tailings which cover the floodplain and extend out of sight downstream, it is a place of such appeal that you reflexively reach for a fly rod, or look around for a place to pitch a tent. Whereas the pillows at Auburn are so extensively crushed that only a specialist can reassemble them in the eye, the pillows of Timbuctoo are rotated but undamaged. Each about two feet in diameter, they are simple in form, elegant, ovate—a spread of huge caviar. Nowhere on land, Moores said, will you see pillow lavas more perfect than these.

  Timbuctoo was a placer camp in 1849. When Moores and I first stopped there, in the nineteen-seventies, we read these words on a wall of a roofless masonry building:

  GOLD DUST BOUGHT

  WELLS FARGO & BROTHERS

  And, barely legible in fading paint, “Stewart Brothers have for sale dry-goods, boots and shoes, ready-made clothing, groceries and provisions.” That structure was all there was of Timbuctoo, where twelve hundred people lived in the eighteen-fifties. Now there is even less. The Wells Fargo building has collapsed. One masonry corner juts chimneylike above the rubble. The words are gone, and only a hill beside the river retains an indelible scar, torn out by hydraulic mining as if by rapid landslide.

  In or close to the magma chambers under oceanic spreading centers, seawater, which has descended through fissures, dissolves metals (copper, silver, iron, magnesium, gold); it carries the metals upward and precipitates them on top of the new rock. If the new rock, in its migration, happens to end up on a continent, the metal comes with it. In the suturing process, faults form. Deeply circulating groundwater redissolves the metals and redeposits them in quartz veins in the faults. In this way, Moores said, it made sense to imagine that the Mother Lode gold of California came in from the deep ocean riding the Smartville Block.

  Smartville, California, is a living town, 95977. It is just uphill from Sucker Flat and a mile from Timbuctoo. Sucker Flat was named for Illinois. The miners looked upon Illinois as “the Sucker State.” Jim Smart, of Smartville, was not from Illinois, and he was smart enough not to be a miner. He ran a hotel. Never mind that the Sucker Flat Channel, between Timbuctoo and Smartville, yielded two and a half million dollars in gold. There is a white wooden church in Smartville, its paint peeling. There are two gas pumps under a sign that says “Bait.” There are slopes of brown grass under blue oaks—and the houses of a hundred and fifty people. Roadcuts in Smartville are ful
l of bulging pillows.

  In the roadcuts of Rough and Ready, nine miles from Smartville, we saw massive gabbros. Rough and Ready was founded by forty-niners, and its citizens soon voted to secede from the Union. If geologists of the nineteenth century and the first three-quarters of the twentieth century failed to see the intrinsic bond between the gabbros of Rough and Ready and the pillow basalts of Smartville and Timbuctoo (and the relationship of those rocks to the diabase and plagiogranite and serpentine nearby), Moores was sympathetic. He said, “If you found a headlight, a hubcap, a brake drum, and a radiator, you would say, ‘Ah, pieces of an automobile.’ But if you had never seen those things assembled you would not relate them to each other. The ophiolitic sequence is one of the most classic things of importance to the plate-tectonics story. Its emplacement is evidence of the spreading process and of the subduction process, not to mention the consumption of vast amounts of ocean crust. There are ten thousand square miles of ground here with no one arguing about the fact that it’s island-arc material. The original arc may or may not have been the size of Japan, or the Philippines, or the Marianas, or the Antilles, or the Aleutians. But it was surely an island arc, and its arrival is signalled by these ophiolitic rocks. If ophiolites are found at the suture of the Urals—as they are—it means that there was a sea between Siberia and Europe. The sea was consumed. Ophiolites were emplaced. And the Urals are welded in a Permo-Triassic suture. Before the Permo-Triassic, in the sea and the islands, the Gulag Archipelago was real.”

  Moores was doing postdoctoral work at Princeton University, in the middle nineteen-sixties, when he first heard about what was described to him as “a wonderful complex on Cyprus,” but when he tried to look it up he could find no data. He requested, from Nicosia, memoirs of the Cyprus Geological Survey. This was at the time when the theory of plate tectonics was in its coalescing phase. The term itself did not yet exist. Oceanic spreading centers were known, and the consumption of ocean crust in subduction zones was beginning to be understood. The idea of a suite of rock called an ophiolite had been around in the science for many years but had not yet been widely accepted or related to the new theory. As the story of plate tectonics further unfolded, the story of the ophiolitic sequence would accompany it like an echo.