A Crack in the Edge of the World (20 page)

The maps he produced and oversaw during the survey were peerless for their time; his reports are classics still; and his tenure as the second director of the Geological Survey—once he had completed the survey he succeeded Clarence King in a post that made him unchallengeably the most powerful scientist in America at the time—was marked by innovation and discovery on a breathtaking scale.

Powell was, however, a keen environmentalist. His appreciation for the great outdoors and for the peoples who were indigenous to it, and his belief in the need to explore rather than to exploit, in the benefits of preserving rather than plundering (beliefs that were personified by such figures as the great Scotsman John Muir, who went on to found the Sierra Club, and such painters of the wilderness aesthetic as Thomas Moran), won him more enemies than friends. His eager support for the preservation of Indian culture, his abiding preference for sensible and sustainable development, and his obsession with the value of water in the West proved too much for many of the settlers, foresters, and miners who were heading in that direction simply to exploit the country. Increasingly Powell came under vitriolic attack from the unconcerned pioneers, and he retreated into a shell, languishing in a world of science and philosophy that was more comforting than controversial. He died a disappointed man at the age of only sixty-five. However, his profile in bronze presides at the South Rim of the Grand Canyon today—watching serenely over that mile-deep chasm of raw cordilleran geology, hoping that his successors take good care of all that he first explored.

The immediate legacy of the four Great Western Surveys—the realization that western America was profoundly different, geologically and topographically, from the rest of the country—was the birth of what was then considered almost a brand-new science. This came to
be known as cordilleran geology, the study of the rocks that make up the extraordinary complexity of the American West. Specifically named societies, journals, conferences, university departments, and offices by the score were created to fill the needs of this new discipline; and when researchers gaily described themselves, without much fear of challenge, as “cordilleran geoscientists,” everyone knew what that meant.

But, for all the romance and intellect brought to bear on the region, until the birth of the New Geology, cordilleran geology resulted in precious little fundamental understanding of what was going on there. The initiation of a real understanding—a post-tectonic-plates-New-Geology kind of understanding—came with one classic academic paper that was written and published in 1970.
*
It was a paper that would have given no clue to any lay reader, considering the recondite language of its title: “Ultramafics and Orogeny, with Models of the U.S. Cordillera and the Tethys.” But its publication produced a tipping point in the comprehension of western American geology—and it made the career and reputation, many would say, of the one figure who today is most prominently associated with the arrival of the New Geology in the West. The author was Eldridge Moores, who, even envious colleagues will acknowledge, remains the best-known member of the geology department—he is now an emeritus professor—at the University of California's campus in the Central Valley, at Davis.

THE BASIC QUESTION
that would niggle away at anyone working on the rocks and structures of the western states of America was simply:
Why?
Why this? Why here? How come?

It is something that probably any westbound traveler would ask as well. The plains over which he has been moving for days have been hot
and dry and endless and flat—and then suddenly, as if out of nowhere, a mountain range! It is climbed, surmounted—but then beyond it on the horizon there appears another, and beyond that a stretch of a desert, then another range, and then a network of canyons and waterfalls, and a farther set of monster mountains, and yet more and more scenery that is so spectacular and so utterly different from anything that lay behind, or anything that was even imaginable in the America already seen and known, that any wanderer with any sense of curiosity would be bound to ask that selfsame question, too: just
Why?
What force could possibly have compelled the world to do as it has done out here—just why is everything such a confused mess, so unsettled, and so manically disarranged? Why this? Why here? How come?

Eldridge Moores was one of the first to come up with a credible-sounding answer. It is an answer that hinges on a very special sequence of rocks that is found in many places in western America and in a number of other geologically fascinating (and, as it would later be revealed, structurally similar) parts of the world, and that invariably incorporates three distinct types of material.

There is always in each sequence one great thickness of very dark-colored volcanic rocks that includes lavas like basalt or their coarser-grained kin called gabbro; there are always a number of beds of deepwater shales and often a particular type of sedimentary rock known as chert, frequently complete with the fossils of plankton and slightly more preservable sea animals called radiolarians; and there is most essentially and most invariably a sequence of hard and greenish-colored speckled rocks that have markings in and on them that vaguely resemble the skin of a snake. Because of this resemblance this one particular rock has been called
serpentine
, a name it was first given in the fifteenth century.
*
The three-rock sequences that then incorporate
this serpentine—the sequence usually runs, from the bottom upward, serpentine-gabbro/lava-sediments (including chert)—are currently known by a combination of the two Greek words
ophis
, for snake, and
lithos
for rock, which gives us the highly distinctive snakelike rock,
ophiolite
.

The fact that such sequences of rock were very common to mountainous regions, especially the European Alps, was first recognized by the great nineteenth-century German geologist Eduard Suess. Another Alpine geologist named Gustav Steinmann then pinned down the three essential components, and for most of the first half of the twentieth century the sequence was known as “Steinmann's Trinity.” Calling them ophiolites came about in the 1930s, once it was realized that the sequence—serpentine-gabbro/lava-sediments—was to be found in glorious display in geologically contorted areas all around the world, with ophiolites discovered in the Alps, in Oman, in the Troodos Mountains of Cyprus, as well as in the magnificently disarranged mountain chains of western North America and, most specifically of all, in California.

It is this unfamiliar word—though
ophiolite
is now a word known to all practitioners of the New Geology—that lies at the heart of what Eldridge Moores realized. It refers to a concept that is tricky to explain, but that, once understood, answers all the basic questions relating to the makeup of the American West and, most particularly, to the structural peculiarities there that led to all the San Francisco earthquakes, culminating in the disastrous event of 1906.

Professor Moores remembers the moment of his realization only too well. It was December 20, 1969, and he was in Pacific Grove, California, at the Asilomar Conference Center. He was listening, fascinated, halfway through a session of the second of the annual Penrose Conferences that the Geological Society of America now holds to ruminate on the most important new developments in earth science.
*

At this legendary gathering “the full import of the plate tectonic revolution burst on the participants like a dam failure,” he later wrote. Paper after paper was being read that overlaid the new theories on top of virtually every major process of geology that had shaped the planet—the location of volcanoes, the folding of mountains, the distribution of earthquakes, the shape of the continents, the history of the oceans. Everything was being answered by this devastatingly simple notion: that plates floated about on top of the plastic mantle and collided with one another, scraped alongside one another, broke into pieces, or welled up under the influence of the immense heat from below. The “marvelous dance of the plates” is how one of the conferees put it, with the rapture of the collective
Eureka!
It was, reflected Moores, “one of the most exciting moments of my life,” and everyone else at this most remarkable gathering of geologists appears to have felt the same. Asilomar was a turning point in science like few had ever known.

His own moment came as he was listening to the conference convener, Bill Dickinson, presenting his summary. Moores had drifted off message for a moment, thinking about a discussion the previous evening about just where the world's ophiolite sequences were, when, “in a blinding flash of insight, it came to me.” What came to Eldridge Moores would make him famous, in two distinct worlds. He would become well known throughout the geological community, one of the revered figures in the story of how a new science gave new answers to a very old question: How did the world as we know it come about?

And he became famous much more widely among the lay community thanks to a book that was written about him by his old friend and Princeton colleague, the similarly legendary John McPhee. The book,
Assembling California
, became a bestseller and remains a classic today.
Few are the academic geologists who have ever enjoyed the kind of fame that is currently enjoyed by Eldridge Moores. And that he is so well known is in part because of the sinuously elegant prose by which McPhee describes him—but also because, although the concept of ophiolites may seem at first a little cumbersome, the explanation of what Moores realized—how ophiolites fit into the story of plate tectonics and how they answered the three questions
Why this? Why here? How come?
—is, thankfully, very much less so.

For, basically, he grasped that each of the ophiolite sequences that
are found today in the mountains of the West are the remnants of ocean floors. They are remnants of oceans floors that have been bounced, to put it most crudely, up on top of the continent. They have been bounced up in wave after wave as the tectonic plates—and that in relatively recent times means the North American, the Farallon, and Pacific Plates or their various antecedents—have collided with one another over the eons past.

Moores made his deduction simply by thinking about the nature of the three kinds of rock that made up an ophiolite—wondering why such strange and exotic rock sequences were sitting up on the mountaintops in the middle of a continent. After all, at the
base
of each sequence are the serpentines and coarsely crystalline igneous rocks that we know underlie all of the world's oceans. In the
middle
of each sequence are the “green rocks,” the minerals of which have been subjected to a moderate amount of pressure and reasonably but not terrifyingly high temperatures, and so can be said to have been altered by a series of moderate geophysical events—they have not, for example, been hurled down to the edge of the mantle and tortured by the extraordinary pressure and heat that is found there. And at the
top
of each sequence are the lavas and then the chert-rich sediments, deposits evidently made by deep seas and that include the sieved-out remains of seawater itself.

What Eldridge Moores deduced from this complex mélange of rocks is a sequence of events that is exactly consonant with what is now known about plate tectonics. He was able to declare that the geological confusion so readily apparent in the Rockies, the Sierra, and all the other mountain chains of the West is in fact no more and no less than the result, time and again, of neighboring plates bumping into each other. What then happens depends on local circumstances. Material on one plate dives underneath the material of the other plate: Some of this melts as it does so and then (because it is so light and volatile) forces its way back up toward the atmosphere; some of it rides up and is scraped off onto the upper side of the other plate; and some of it slides past the other plate and is scraped off onto it in a similar manner.

The basic narrative is exceptionally simple: The plates bang into each other, and, where they do so, large amounts of material are dislodged and stay put, being heated and compressed by the enormous forces of the collision. Then the collision abates, and the plates reorganize and regroup for another assault—and the foreign material that is left behind, so mixed and contorted and folded, is already, or in time becomes, a mountain chain—ready to have another mountain chain piled on alongside it when the plates collide once more, and yet another when it happens again, and again and again and almost endlessly (since there is so much time in geology) yet again.

Each of these foreign rock slabs or slices or sequences—some of them hundreds of miles long and dozens of miles wide, and many now spearing up into the cold and snow-rich air of the upper atmosphere—is now known as a
terrane
, a word confusing because of its homonymy with the word
terrain
, and which means landscape. But a terrane is a piece of continent or ocean floor that is foreign—it is, to use the term more favored by today's geologists,
exotic
. It is a piece of the geological somewhere that is now settled in a place scores of miles—maybe hundreds or even thousands of miles—from the geological somewhere else where it was made, or from where it once existed. The West of America is full of such terranes, and full of the ophiolite sequences that embrace them or that they in turn embrace. Most of these bodies or sequences trend north and south in great elongated ranges of mountain peaks that fill the windshield when you are driving west, and that etch the land below when you are flying across America toward the Pacific Ocean.

And they trend north and south because they are the result of collisions that occurred millions of years ago, either between three north-south-trending plate edges—those of the Pacific and Farallon and North American Plates, whose edges very roughly parallel the Oregon and California coastlines that exist today—or between their antecedents, that formed other oceans and other continents, such as Pangaea and Rodinia and Kenorland and all the other bodies and seas that composed the earth in times that, unlike mankind's own history, were truly ancient. These bodies moved headlong into one another,
banging, diving below, arching up, retreating, and banging into one another again, with one of the plates heading from the west toward the east, the other moving slowly but with immense and unstoppable power from the east toward the west. And all of these bodies and plates were compelled to move by the convection currents in the earth below, currents that are churning ceaselessly and that are making the plates execute these unending mazurkas and tarantellas up above on the mantle top.