A Crack in the Edge of the World (6 page)

Spain, religion, soldiering, rambunctious literature, and the tribes of the Miwok—so much of early California distilled into one small Mount Diablo story. Small wonder that I kept my Coleman lamp guttering, and my pages turning, well into that breezy summer night.

THE DULLARDS WHO WANTED
to christen the mountain Coal Hill had a point, however. The rocks of Diablo were, by the middle of the nineteenth century, throwing up all manner of mineral wealth, and not a few people were beginning to make modest fortunes.

Throughout Northern California there had been a lively interest in mining—one might almost say a quietly fanatical obsession—ever since that January morning in 1848 when a misanthropic carpenter from Lambertville, New Jersey, named James Wilson Marshall, discovered a scattering, a
blossom
, of gold flakes in the millrace of John Sutter's lumber works near Sacramento, inadvertently triggering the Gold Rush, which in essence created
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the state of California. In these fairly metropolitan parts—Mount Diablo is only thirty miles from San Francisco, and rather less wild than where other claims were being staked farther afield—prospectors in the hundreds were a-roving in search of minerals of one kind or another. And though maybe in the pleasant purlieus of the hills close to San Francisco Bay there was less of a need for the burro and bedroll, for the claim stake and the slouch hat—the accoutrements of the grizzled caricature of the prospecting type—there was nonetheless a great deal of very energetic exploration of Diablo's riverbeds and the canyon walls, mainly conducted by new immigrants who had come by ship to see what the Gold Rush fuss was all about and stopped at Diablo on their way. Many lingered, and found lodes, outcrops, deposits, and ore bodies; and by the 1860s, as a result of their energies, a series of substantial discoveries had been made that
would turn Mount Diablo and its slopes into a place as spectacular for its buried wealth as it was already magical for its aspect and topographic power.

Coal—dull, brown, dirty, unromantic coal—was the first mineral to be discovered there, peeking seductively out of a thick group of fairly recent sediments known as the Domengine Formation, a band of which lies just to the north of the mountain, in the flattening fields that spread down to the Sacramento and San Joaquin Rivers. Gold and silver, mercury ore and copper, were nearby, too—but their quantities were small, and the difficulty of extracting them was prodigious and at first far too expensive. But coal, on the other hand, was abundant, and soon miners and mine owners realized how they could make their fortunes from it.

For it happened that the discovery of coal on the slopes of Mount Diablo coincided almost precisely with the ending of placer gold mining in Sacramento, forty miles to the east. River sand was washed and the lighter minerals tipped back into the stream, leaving the sparkles of gold behind; even Bret Harte found a nugget worth twelve dollars on his first day of experimenting. But the relative ease with which gold had initially been extracted from the ground was as evanescent as it was seductive. By 1852, a mere four years after Marshall's discovery (which was announced formally by the president, James Polk, thereby suddenly redirecting westward migration toward California and away from the more immediately enticing farmlands of Oregon), the glistening nuggets had all, it seemed, been found. Such gold and silver as might be lurking in the rocks had from then on to be won by more traditional mining methods, with the gold hosed out by the use of enormous jets of water or the hard igneous rocks crushed and hammered and pulverized and blown to smithereens in order to release their bounty.

To do this, the mine owners required machines, big machines, nearly all of them made of iron. They needed rock crushers and pumps, stamp mills and conveyor trestles. They had to lay railway lines and acquire railway cars, as well as immense tracked engines that could claw the rock from the cliffs and tear down whole mountains. All of
these great iron machines and manufactures had to be created. But the East was far away, and the costs and perils of bringing such enormous goods overland to California prohibitive, so a good deal had to be made locally. There had to be foundries and forges and rolling mills and factories in Northern California, with their primary function to keep the gold and silver mining industries alive—to help make the growing dream of California into a reality, and not let it die prematurely, a chimera.

All of these new factories depended upon a source of heat—a source that helped to smelt and puddle and make the steam and turn the wheels and fans and conveyor belts. And that source, of course, was coal. Not the eastern and foreign coal that was then being brought in by ship for $30 and $40 a ton—but the newly won and homegrown Californian coal, carted in from the Mount Diablo mines that were, come the 1860s, being dug, drilled, and blasted into the foothills between the peak and the two rivers to the north. Using locally mined coal would make the factories of San Francisco and Sacramento hum, and hum for a sound return on the backers' investments.

It was a short-lived experiment. Only 4 million tons were ever extracted from the Diablo mines; competition from cheaper and more accessible coal farther east put paid to the California coalfields. Before long such pithead communities as had sprung up were abandoned, doors left open and swinging on their rusting hinges, stores emptied and their windows broken; wild grasses and chaparral engulfed the outhouses. Some say all that remains today are the trees that miners brought with them to cheer up their dismal work camps, among them black locust trees, almond bushes, and a fast-growing weed known as ailanthus, or tree of heaven, which was brought in by the Chinese shopkeepers and grew in such wild profusion that it is now regarded as a blight, fit only to be slashed and burned and carted away by the ton.

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.
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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.