A Crack in the Edge of the World

  There is a tendency common to most of us to take the more modest of our landscapes for granted. We see a wide and fertile plain, and we drive across it, as fast as its flatness allows, rarely pondering what might have brought it into being. We come across a valley, and, though we might take pleasure in its appearance, we give it all too little thought, other than perhaps to assume there is probably a river somewhere within its folds. And, while we are generally awestruck by the more spectacular mountain ranges, it seems true to say that those hills that are simply hills, or those mountains that are simply mountains, rarely prompt us to ask: Just why are they there? What forces first made them and set them down here, in this particular place?

  Mount Diablo, though its isolation makes it somewhat more dramatic than most, is just such a place. It is a mountain generally outside the orbit of popular consideration, big enough to be of note, too seemingly ordinary to be puzzled over. To its neighbors in towns like Concord and Antioch and Walnut Creek, who can so readily see its bulk from their picture windows, it is simply a piece of scenery, an eternal and unyielding part of the view. Very few people ever stop to wonder why this particular mountain is where it is; what forces caused the land to slope upward as it does. And yet those forces, their complicated workings all encapsulated in the geologic history of this one mountain, are part of the same set of forces that caused the destruction of San Francisco. To understand this, to understand Mount Diablo, is to begin to understand why California, perched precariously at the edge of the North American world, has been destined by its geology to be both so beautiful and so dangerous.

  Like most, I had given precious little thought to such things on that summer’s evening. As I drove up through the gloaming along the winding mountain roads, my interest in the hills, such as it was, related simply to my need to muster sufficient horsepower to overcome them. To me that night—and to countless others who were seeing the hillside every day, and who might have paused to wonder why it might be and what it might be—volcano was perhaps the explanation that most readily came to mind, especially in the American West, where such things are much more commonly seen. The shape of the mountain when it is viewed from afar—a low double cone, which from the Central Valley side seems to rise spectacularly alone out of the plains like an Etna, a Vesuvius, or a Mount St. Helens—rather reinforces the impression.

  But Mount Diablo is most certainly not a volcano. Few places in the world are as geologically complicated as California, and few parts of California’s underside are as raggedly confused as Mount Diablo. And though the story that will unfold in later chapters has to do with geological structures and happenstances that involve San Francisco, Santa Rosa, San Jose, the San Andreas Fault, and a host of other faults besides that are some distance away from this rather peaceful-looking mountaintop, the saga of why Diablo is where it is and what it is has in fact great relevance to the geology and the geological processes that once destroyed San Francisco and that may yet destroy it again.

  THE GEOLOGY OF the northern half of California—whether we are talking about San Francisco Bay or the Central Valley, the Coast Range or the Sierra, the Monterey headlands or the coast of Humboldt County, or Mount Diablo itself—is all interlinked, subtly, confusingly, and, for the geological mapmakers, often maddeningly. These links go far beyond the borders of the state—political lines that pay no heed, in this case, to the absolutes of geology.* They spread far, far beyond—as we shall discover, they reach up to Alaska, they percolate across to Wyoming and Montana, they reach back west across two oceans as far, in fact, as India and Australia. One might say, indeed, that the story of what makes California so complex and so interesting and so dangerous—and what makes Diablo so similarly geologically alluring—has implications for, and connections to, the planet in its entirety.

  About 170 million years ago—in the early to middle part of the Jurassic, when dinosaurs were the dominant large land creatures in other parts of the world—the floor of what we now call the Pacific Ocean began to spread outward, eastward and westward, from a central suture line. The section of the floor that moved east did so with such force and speed that about 50 million years later—120 million years ago—it collided, gently but powerfully, with the cliffs and mountains at the western edge of what we now call North America. When that almighty crash occurred, two things appear to have taken place.

  First, a sliver of the ocean floor, which happened to be made of rocks that were somewhat heavier than those of the cliffs and hills of North America (thus causing it to lie so low that the ocean was able to accumulate above it, while the American hills seemed to float, almost ethereally, in the air above), was forced downward, sliding under the cliffs and hills like an envelope being pushed surreptitiously underneath a carpet. And second, while it was being slipped underneath, it dragged down with it all the sand and soft rock that had accumulated on top of it while it had been moving eastward from the center of the ocean. It had traveled a long way to the point of collision—perhaps 5,000 miles—and it had taken a long time to arrive—perhaps 50 million years. The result was an ever-moving floor with an unimaginably large thickness of accumulated material on top—and some of it dipped under, carrying with it the floor material, while some stayed offshore, like surplus froth scraped off a cappuccino. It remained like a great barrier of islands, well to the west of the place where one plate was sliding under the other.

  Thus a basin was created between the hills at the point of collision and the hills of the offshore islands—with the former (to reiterate) being a complicated and multilayered arrangement of ocean floor together with mixed-up and younger sediments, the latter being rather more entirely youngish mixed-up sediments with little or no ocean floor anywhere around, other than deep, deep down below. And over the next many millions of years, more sediment accumulated in the basin, the makeup of which was determined by how it was accumulating (whether in silt-rich rivers, on some sandy shoreline, by settling on the bottoms of deep oceans, or born from onetime marshes or long-buried sand dunes) and what the weather was like while it was doing so (warm and humid or freezing and dry).

  There must have been one period, about 40 million years ago, when huge ferns and soft trees crashed, dying, into warm and fetid swamps. The layers of material in the swamps were then compressed and buried and heated, and after time and maturation they produced the coal of the Domengine Formation for which the miners hunted so assiduously in the 1860s. But there were other periods when there were deep blue seas instead of botanically rich swamplands, and they were alive with shellfish, sharks, and other noble creatures; and there were other more recent times when mastodons and saber-toothed cats trekked over windy grasslands and left their bodies to rot and become skeletons in forests of trees that seem not dissimilar to those growing in California today.

  And then, 20 million years or so ago, the oceanic plate suddenly changed direction, for reasons that will be made clear (or as clear as the science will allow, since much remains unexplained) in a later chapter. Instead of pushing eastward, to smash head-on into the cliffs and hills of North America, the oceanic material began to move northwestward, proceeding smartly up alongside the coast, scraping past it instead of plunging underneath it.

  The connection with San Francisco now becomes clear, for this new movement is exactly the same movement between plates that would go on to produce the cracks in the earth’s surface that nowadays trigger the myriad earthquakes that occur farther to the west. At Mount Diablo, though, the movement did something rather different: It caused all the material that had plunged below the North American Plate to be ripped northward, bringing it hard up against the newer sediments that had been accumulating behind where it had been diving downward. The newly arrived material began to wrap itself around the older crustal and downthrust rocks, as if it were an immense shell of pastry. In time it buried the older material entirely and made it more or less invisible, coated in a thick covering.

  And there this material would have remained, excep
t that about 4 million years ago, for reasons that will also be explained later, the whole mixture was dramatically folded upward. The old, hard rocks were in the center of the fold; the new, young, soft sediments were on the outside. Under the influence of weather the young, soft rocks were swiftly worn away, thus exposing, as a range of steep and dramatic hills, the core of ancient ocean floor and dragged-down sediments from the dinosaur-era age of the Middle Jurassic. Mount Diablo was born. The soft rocks, which in one particular case were thick with abundant layers of soft coal, were to be found on the flanks of the hills; the unyieldingly hard and relatively ancient rocks, which were good for road stone but not at all rich in the kind of minerals that make men wealthy, were left in the middle.

  The crucial element of this long and complicated story is the relatively uncomplicated but still somewhat mysterious event that took place almost exactly 20 million years ago: the moment when the onward press of the ocean crust suddenly, and for a reason that long remained a mystery, translated itself into a northward, sliding motion—as when an army suddenly wearies of charging head-on at the enemy and begins to execute a mysterious, somewhat cunning motion to one side that appears to be an attempt to outflank the foe. At this point—which took place in the middle of the period of world history known as the Miocene—everything that now in essence defines seismic California was brought into being.

  This was the moment of making—when the earthshaking, city-killing, history-creating, epoch-changing linear system, 750 miles in length, and known since the beginning of the nineteenth century, broadly and generically, as the San Andreas Fault, was created. That the oncoming plate’s change of direction also helped to create this hill, the massif that rises so formidably in the picture windows of the residents of the towns of Clayton, Pittsburg, and Pleasant Hill and their like, reinforces the view that I started to hold in the tent that breezy night: that Mount Diablo is more connected and interlinked with the events of the San Francisco tragedy than almost all those who live beside it and below it have ever properly supposed.

  BY NOW I WAS READY to sleep. I stepped briefly out of the tent and looked up at a sky ablaze with stars: Cassiopeia and Gemini unusually bright, Castor and Pollux winking down from the roof of the universe. There seemed to be a gathering of clouds rolling onshore from over the faraway Pacific. The loom of lights from the cities spread a blush of orange-pink on the underside, making them glow bright against the velvet of the coastal night.

  DAWN CAME UP all too early that next morning, and from where I was camped, close to the top on the western side of the mountain, the day and its morning sky were pale blue and clear as crystal. There had evidently been a shower in the small hours: The fire was out, the ashes were damp and cold, the pine needles glistened with more than the usual dew. I walked up along the empty road (the gates below would not open for another hour, and so I could revel in the knowledge that I still had the mountaintop entirely to myself) to the summit. At the top is a immense octagonal stone building—a onetime aircraft beacon,* a uniquely visible landmark and, as it happens, a memorial to one of the defining periods in recent American history, the Great Depression. The building, fashioned from a highly fossiliferous sandstone quarried locally, had been erected in the 1930s, using the brawn and muscle of scores of out-of-work men who had been organized into a local chapter of the federally funded Civilian Conservation Corps, and who had lived for two years in a camp close to where I had slept the night before. I climbed the steps up to the parapet and gazed, silently and dumbstruck, at one of the most stupendous views in all America.

  William Brewer, when he first surveyed the mountain in 1862, estimated that 80,000 square miles could be seen from the summit. “I made an estimate,” he wrote in his report for the Geological Survey, for which he was principal assistant, “that in tolerably plain view the extent of land and sea embraced between the extreme limits of vision range over 300 miles from north to south, and 260 to 280 miles from east to west. Probably but few views in North America are more extensive, and certainly nothing in Europe.”

  There was no haze, no smoke from forest fires, no fog, no pollution—at least, not where I first looked, toward the southeast, almost directly into the rising sun. The dry flatlands of the Central Valley spread out brown and cornrowed, with their arrow-straight irrigation canals gleaming like tinsel. Beyond them in the distance, forming the horizon, rose the jagged and snow-topped wall of the Sierra Nevadas, a range that stretched 250 miles from the Cascades and Lassen Peak in the north to China Lake and the fringes of the Mojave Desert in the south.

  This immense wall of rock was where California’s two most precious assets were created: its water and its electricity (though more properly only one of these was a real asset, since the latter was created by the former, provided that the water was above sea level and thus possessed of potential energy). The moist westerly winds that blew in from the ocean were stopped in their tracks by this great granite massif, which, happily for the state (though less so for that part of California known as Death Valley as well as the entire western part of the state of Nevada, which lies in the mountains’ rain shadow), proved too high for the winds to climb over, too elongated for them to weave their way around. The snows that then fell so constantly in due course melted and became rivers, with the waters then employed either to slake thirsts or to create power.

  Most of the range I could see, and, had I had a detailed chart, I imagine I could have recognized the noblest peaks: Mammoth, Dana, Gibbs, Parker, Darwin, Lamarck, and the great summits around Yosemite. The very highest, Mount Whitney—named for the first head of the Geological Survey—was too far away to sight, but, had I known exactly what I was looking at that morning, I daresay I could have made out far to the southeast Mount Brewer, the 13,500-foot Sierra peak that had been named for the remarkable and heroic William Brewer, an explorer of (according to his biographer, Francis Farquhar) “the strongest fiber, of unflagging energy, the soundest judgement, the utmost tact, and of unequivocal honesty and loyalty.”* He was also accorded the honor of having the California spruce, Picea breweriana, named after him; but he is otherwise too little remembered, like so many of those who opened up this staggeringly beautiful country, and who beckoned to outsiders to come west for reasons aesthetic and not purely mercantile. John Muir and Ansel Adams were first among those who heard this call, but many of the rest of early Californians, one is often tempted to suppose, belonged to the more strictly practical school of migrants.

  I turned away from the sun, to my left, and gazed up to the north—a view dominated initially by the most spectacularly severe of California’s peaks, the ice-covered, glacier-strewn, and symmetrically perfect cone of Mount Shasta. Shasta’s standing, like that of Mount Kailash in Tibet, stems from its magnificent isolation: It is a double volcano, and it rises, without warning, from where the Central Valley peters out, close to the logging town of Redding, which was also just visible from that morning’s vantage point.

  Much closer, and just below Diablo’s slopes, were the two great rivers that most properly delineate the geography of this part of California; the nearer of the two was the San Joaquin, which I could see faintly, squirreling its way through the great sprawling inland port city of Stockton;* the more distant was the Sacramento River (the Río Sacramento, or the “River of the Sacrament”), which coursed down from the north, and from the mountainsides behind the state’s present-day capital. The two joined in plain sight below me in a wide bay and glinting marshlands; and then, after squeezing their combined way through the Carquinez Strait—named after the Indians who had given the missionizing Spanish soldiers such a hard time with their diabolical medicine man—and beneath the iron highway bridges on which I could already see the crawl of morning motor traffic, their waters spread out into a wide and flat declivity: the immense, 1,600-square-mile tidal harbor that unfolds from the hills, valleys, wineries, sheep farms, and flower meadows of Napa and Sonoma in the north, down to the plants, factories, airfields, think
tanks, and next-century-paradigm-shifting industries around Palo Alto, Stanford, and San Jose in the south.

  There the rivers widened at last and evolved lazily and muddily into the feature that, once its value as a harbor was realized, was enthusiastically named to honor Saint Francis of Assisi, Bahía San Francisco, San Francisco Bay.

  And center stage, seeming almost to be floating out on the wide waters, stood the city, the obvious and very evident capital of it all. There, at last, was my goal, the first sight of my destination, of the great city that had always been the Bay’s principal port. It had at first been called after the pretty shrub that grew there in such abundance, yerba buena. But in 1847, in commemoration of the universally venerated twelfth-century priest from Assisi in whose kindly principles its founders so ardently believed, it had been given the name it bears today: San Francisco.

  What I remember most about the city, which was spread out beyond the low hills and clustered like a jewel box of gleaming spires and glittering windows on its tiny thumbnail of a peninsula, was just how astonishingly delicate it all looked. It was quite unlike New York or Chicago or Boston. Those places were gray, massive, battleship-like cities, cities that were indelibly written into, and indestructibly welded onto, their landscapes, each fully a part of the topography that once shaped it. London, nestled among its own enclosing hills, had looked and felt much the same for centuries. As had Berlin, Paris, Moscow. And Rome, of course, “the eternal city.” Tokyo, so ancient and so modern and so always there, regardless of the fires and wars that had scourged it. Even Hong Kong, Sydney—even such defiantly modern cities as these had acquired a look of settled permanence.