A Crack in the Edge of the World (25 page)

The big worry among local residents is that, somehow, the drilling program itself will trigger an earthquake. There is a widely held concern—held, at least, among those who are somewhat skeptical of science—that interfering with the delicate balance of the plates will start something that might prove unstoppable. Was it not possible, some vaguely exercised Californians asked rhetorically, that the drilling rig might set something off? The USGS said there was no possibility. Look at Texas, someone said. There can be no more comprehensively drilled place than the oilfields of Texas—and yet the state is seismically almost stone dead.

Leaving aside the questions begged by such a statement—Texas is basically very much more geologically stable than California—it turns out that the skeptics did have some cause for concern. For it so happened that the SAFOD drill site was at its most active, and the drill bit was probing most closely to the fault, when, on the morning of September 28, 2004, a magnitude 6.0 earthquake hit Parkfield square on.

It was the largest earthquake to strike the town for thirty-eight years. The USGS and the drill team insisted there was no connection. Locals were not so sure.

THE COUNTRYSIDE SOUTH
of Parkfield rapidly becomes very much drier, sandier, and unpopulated. Only eight inches of rain fall each year on the Carrizo Plain—a high, hot place of salt flats and soda lakes, with kangaroo rats and leopard lizards and other improbably named fauna—but with almost no trees and little vegetation to obscure what the fault does on its way through. The result is that the San Andreas is laid bare as it pushes down along the desert, as if pinned to a dissecting table. Almost all books related to the fault sport an aerial photograph of its signature across the Carrizo Plain on the jacket, so clear and obvious is its passage.

But, leaving aside the scimitar-like line it cuts across the scenery, it is the right-lateral displacement of the rivers running across the fault
that presents it in an even more dramatic light. Such oddities show the San Andreas not merely as a static entity but as something that shifts:
E pur si muove
.

To the east of the plain rise the low hills of the Temblor Range, and from their upperworks course innumerable rivulets—usually dry—known locally as washes. On those rare occasions when rain does fall, these washes fill up with water and form raging streams, which rush downhill, carving deep canyons from the loose and friable soil as they do so. The dry ravines that are left behind are known as arroyos, and, were the hillsides perfectly geologically stable, one would regard such things as merely pretty, the serried ranks of parallel valleys proceeding from summit to valley floor, peculiar only in their number and symmetry.

But the edge of the hills marks the line of the fault. The Carrizo Plain happens to be on the Pacific Plate, and the Temblor Range is on the North American Plate. Every so often the Pacific Plate jerks itself northward, and when this happens it takes with it the paths of the arroyos, just where they begin to run across the plain. Where this has happened the effect is startling: The ravine starts off running downhill, then suddenly turns ninety degrees and begins to flow along a straight line parallel both to the edge of the range and to the valley floor—or, to put it another way, parallel to the line marking the joined edges of the two plates. It goes on like this for a few hundred feet—and then with equal suddenness it turns back ninety degrees, flowing in its original direction once more.

And every stream does the same—in echelon, every single stream exhibits the double jog, each in the same direction, each serving as a marvelous reminder of the fact that the fault moves and of the direction in which it does so.

This is not to say that the movement along the fault is horizontal only—which is what a cursory look at the offset streams of the Carrizo Plain might imply. There is a vertical component, too—the Temblor Range, for example, has been caused by vertical uplift along the fault. (The reason it exists at all is that the fault does not exactly coincide here with the direction of plate motion: It is slightly skewed to one
side, and as a consequence of this skewing the material bunches up, like a pleat in a carpet, as the plates move alongside each other.) But in this part of the San Andreas the horizontal component far outweighs the vertical, by a factor of between 10 and 20 to 1.

One of the most dramatically offset of these Carrizo Plain streams—a stream that has become the poster child for all San Andreas phenomena, so clear-cut is its display—has been named Wallace Creek, honoring the field geologist who has perhaps been most prominently associated with the fault, Robert Wallace of the U.S. Geological Survey.

It was Robert Wallace who reversed a notion among some geologists that had become fashionable during the mid-twentieth century: This was, that since the newly invented machine called the seismograph gave all the necessary answers about earthquakes, there was little need for geologists to go out into the field to study them. For years around the middle of the century, quakes were primarily in the purview of white-coated technicians, people sitting in air-conditioned laboratories working their bloodless mathematical wizardry to determine the nature of the spasms that occasionally afflicted the earth. Robert Wallace changed all that: Armed with a hammer, a compass, a series of very good maps, a tent, and endless cans of beef stew
*
—which he liked to eat cold—he went back out among the rocks and worked for years to delineate the fault as it charged southward from the Carrizo Plain.

He mapped the places where the fault exhibited what has come to be known as the Big Bend—the long and lazy turn it executes midway along its length, which gives the San Andreas its approximate overall shape of a boomerang. To create this bend, the line first turns through thirty-five degrees to the left—to the southeast, that is—then lazes back again toward the right, until finally, sixty miles of zigzagging contortion later, it settles straight, back on its original track.

The turn is made as it traverses an unusual set of mountains called
the Transverse Ranges—unusual because, unlike all other Californian mountain ranges, these mountains slice across the state from west to east, and do not parallel the coastlines and the faults, as do the Sierra and the coast ranges, as well as all the lesser ranges like the Temblors and the San Gabriels.

The fault crosses this range at a remote mountain cwm called the Tejon Pass—so named because the Spanish lieutenant who discovered it at the beginning of the nineteenth century found a dead badger,
el tejón
, at the mouth of the canyon—and then passes on into the achingly dry wilderness of the Mojave Desert, close to the city of Palmdale. Robert Wallace was one of the first to work out just how far the fault seemed to have slid in these parts over its millions of years of life. As a brash young graduate student he declared that at Palmdale
*
the two sides had shifted 75 miles apart from each other—a figure that, in those more conservative, pre-tectonic-plate-theory days, was so improbably large that his colleagues chortled in disbelief. They should not have bothered, since Wallace was, of course, almost right—at least so far as orders of magnitude were concerned. The two sides of the San Andreas Fault have moved at least 250 miles apart since it was born—sometimes slowly and steadily, sometimes through the savage interruptions of earthquakes.

California's other truly great earthquake occurred in these parts, close to the Tejon Pass, in the spring of 1857. It was an event that was at least as big, and may well have been even larger, than the quake that was to wreck San Francisco nearly half a century later.

It occurred on April 9, and it had a supposed summary magnitude
of 8.25—just a notional amount less than that later ascribed to San Francisco. Its intensity (which is not the same as magnitude, the distinction being explained in the appendix) is thought to have been in the region of VII, also rather less than the VIII and IX that were experienced in San Francisco. Some calculations insist that it was a greater event than San Francisco—that more energy was released and that the displacement of the ground was far more extensive. But there is so little by way of historical record—much less than that of the New Madrid Earthquake of 1811, mentioned before—that it has to be regarded as an event of less historic importance. It cannot be classed as one of the most significant earthquakes of all time—which 1906 most certainly was, because it ruined so much and killed so many. But it was nonetheless very, very impressive.

Its epicenter was actually nowhere near Tejon Pass. It has since been shown to have been back in Parkfield. But since virtually no one lived in Parkfield in 1857, and since Tejon had an army base, Fort Tejon,
this bleak mountain pass has ever since been put forward to enjoy or to suffer the notoriety.

The base had been created three years before, ostensibly as a means of controlling—the army's word—the resident Indian population. It was little more than a handful of adobe huts huddled among the valley oak trees, beside a stream. The only thing that was unusual about the fort was its small and temporary population of camels, which had been brought to Texas from Egypt and Turkey because some military planner thought they might be useful; they proved worse than useless, however. The Texans got rid of them and sent them to California, and the army in California had no real idea what to do with them either, and they soon vanished. Some still associate Fort Tejon with something called the U.S. Army Camel Corps: There was never, in fact, any such thing.

Just after eight on the Friday morning of January 9, 1857, an almighty earthquake rolled down onto Tejon from the north. Witnesses speak of huge wavelike shakings of the earth; and, though some speak of up to three full minutes of shaking, an unprecedented duration, most agree that it was just some forty or fifty seconds' worth of nightmarish movement that wrecked all the army huts, tore most of the trees from the earth, and killed a woman at the nearby Reed's Ranch. The local Kern River ran backward; fish were thrown hundreds of yards from where they swam in Tulare Lake; long zigzag cracks appeared in the ground at San Bernardino; massive ridges, five feet high and fifteen feet across, rose and started to snake through fields; artesian wells suddenly failed; the Los Angeles River was hurled out of its bed and began, if only briefly, to flow along another channel; and up on the Carrizo Plain the fault jerked so dramatically that many of the rivers coursing down from the Temblors were thrown off course by as much as thirty feet in a matter of microseconds.

The event was felt all across Southern California. It was not felt at all north of Parkfield, perhaps because of the more lubricated nature of the ever-moving fault up there. Had it struck in modern times, it would have caused dreadful damage forty miles away in Los Angeles. But, as it was, only two people (the rancher, and one other man in a village
plaza) were killed; and the 4,000 people who lived in the sprawling village that was Los Angeles got little more than a jostling.

Matters were somewhat more serious in Santa Barbara, then a pretty coastal hamlet of 2,500 thirty miles west of Tejon. Villagers, who were accustomed then as now to an idyllic setting with equable temperatures, balmy weather, and no more than the gentle plashing of Pacific waves, streamed out onto the streets, panicky and terrified at something they could hardly have imagined. In huge numbers they fell to their knees and struck beseeching attitudes (a mode of behavior that seems now to have been supplanted by a need to turn on CNN), then waited anxiously until the swelling vibrations fell away and the cascades of aftershocks abated. The local newspaper turned to doggerel to explain the dreadful majesty of the moment: “How awful is the thought of the wonders under ground / Of the mystic changes wrought in the silent, dark profound.”

The implications of what was truly an awe-inspiring event at Fort Tejon go some way beyond the simple matter of the quake's enormous magnitude. The geometry of the San Andreas Fault's Big Bend has an effect on the local topography that is very complicated and still being properly worked out. But it boils down to one reality: that because the Pacific Plate is still pushing northward on this part of the fault—moving in the same direction, in other words, here as everywhere else on the 750 miles of its length—and because the Big Bend thrusts a prow-shaped bulge out into its path, the effect of the movement is here not simply a sliding-along-the-side affair; it is also a pushing-up-from-beneath kind of movement, a movement that tends to lift the prow of the northbound plate up somewhat and produce a range of hills in front of it.

Uplift like this was noticed up in Parkfield, where another section of the fault had become very slightly misaligned from the plate boundary—and the Temblor Range, as we have seen, was thrown up as the result of that. Here at Tejon the misalignment was evidently more spectacular: Rather than throwing up a low range of hills on just one side of the boundary, the plate in these parts seems to thrust itself head-on into the rock mass, right into the prow-shaped bulge of California,
and has lifted up hills that would in due course become the Transverse Range, hills that look like a giant raft rising up onto the plate's advancing bow wave. The analogy is an imperfect one—the precise nature of what is going on below these mountains is still being analyzed—but in its essentials it holds.

There are other faults working here, too—very ancient faults with names such as the Clemens Well–Fenner–San Francisquito Fault and the San Gabriel Fault, which displaced the surface rocks for scores of miles, tens of millions of years ago; and shallow thrusting faults that never break surface today but that all the time are helping to accommodate the compression of today's plates as they ram themselves together, breaking and buckling like the crush zones in modern cars or the water-filled “impact attenuators” you see at dangerous road intersections.

And it would be idle to pretend that matters get any less complex as the fault spears ever onward, southeastward, passing as it does so along the zone that separates the San Gabriel Mountains from Antelope Valley (where there are countless supersecret defense establishments, making and testing costly warplanes and missiles), past the suburban sprawls of San Bernardino and Loma Linda and Redlands, then through the San Gorgonio Pass with its throbbing forests of wind generators, and along the Coachella Valley, where the elderly rich like to live out their final years in luxury and perfect weather, in communities like Palm Springs, Rancho Mirage, Indian Wells, and Palm Desert.