The High Sierra

GEOLOGY (1)

Batholith and Pluton

To think about the Sierra’s allure I’m going to consider all kinds of things, but will start with the obvious main fact: it’s a mountain range. So geology has to be part of the story.

I’m not competent to go too deeply into this, but some basics of geology will help me to explain its effects on the mind (or at least my mind), a topic which naturally should be called psychogeology. So in this book there will be some chapters devoted to geology, and many more, in one way or another, to psychogeology.

The geological terms I’ll discuss include the following, briefly defined here:

THE BATHOLITH: the whole mass of Sierra granite

PLUTONS: individual blobs of granite that make up the batholith

THE CREST: the long and continuous highest ridge of the range, from which its watersheds flow west or east

DIVIDES: high ridges that tend to run west from the crest, or stand alone

BASINS: high headwater regions held in a curve of ridges

CANYONS: in the Sierra these are mostly U-shaped, being glacier-carved

MASSIFS: high areas isolated by deep bordering canyons

ROOF PENDANTS: older metamorphic rock stranded atop the batholith

GLACIERS: ice rivers and ice fields, mostly gone now

These terms (many already well known) will help me make my claim that the Sierra Nevada is the best mountain range on Earth, if backpacking is the game you want to play. This book will be making that case more or less continually.

There are some good books by geologists about the Sierra, and one great one, by James G. Moore; if you want more detail on this topic, they have it. For my part, I’ll be keeping it simple. I’ll split this strand of the book into short chapters, and insert them in an order that helps me make myself clear.

First up, then, very naturally, are batholith and pluton, because these terms describe the basic substance of the Sierra. How did this big raft of granite get where it is, floating near the eastern border of California, high above the rest of the state?

Mountain ranges are usually the result of one tectonic plate ramming into another one.

It’s interesting to note that before the theory of plate tectonics was developed in the 1960s, no one could understand why mountains even existed. Earlier theories of orogeny, the term of that time for mountain formation, were completely lacking the basic mechanism involved, so their ideas were badly off. As Wolfgang Pauli once remarked about an incoherent theory in physics, these concepts were “not even wrong.”

One theory of orogeny had it that the Earth had been shrinking as it cooled since its birth, and thus the surface of the planet was bunching up in places like the face of a shar-pei dog. Another had it exactly the opposite, that the Earth was still swelling from the action of interior radioactive heat, and as it swelled its surface cracked, releasing lava that poured up and hardened into mountains.

Oh well. In the early twentieth century Alfred Wegener pointed out what anyone could see on a globe, that Brazil and West Africa seemed to fit together. He suggested this could not be a coincidence, that some kind of continental drift must have occurred; but no one could see how that would happen. Then sonar and magnetic studies of the ocean floor in World War II found a mid-Atlantic rift from which the ocean floor seemed to be spreading in both directions. In a rush the theory of plate tectonics came together. John A. Stewart’s Drifting Continents and Colliding Paradigms is an excellent study of this paradigm shift.

By 1975 geologists mostly accepted this new theory of Earth’s history. Big plates of the lithosphere were sliding around under the pressure of convective currents in the mantle below. Intense work since then has refined the picture, and the history of the Earth’s surface going back millions of years has been established. Pangaea, Gondwana, Laurentia—these are previous configurations of the big continental islands, which geologists have been able to work out by computer models and fieldwork. Now we know there are nine large tectonic plates, and about twenty minor ones. Sometimes they’re sliding past each other, sometimes they’re colliding head-on and one is getting shoved under the other, and sometimes they’re pulling away from each other. Much gets explained by this model, including mountain ranges. The Andes resulted from a Pacific plate’s subduction under South America; the Alps show where Italy is shoving under Europe. The Himalayas mark the place where India is shoving under Asia, in the biggest collision of our time.

California’s Sierra Nevada is the result of the Farallon Plate subducting under the main mass of North America. It got shoved under and began to melt about 120 million years ago. Just the rounding error here is several million years—think of that! It’s one of the stunning facts of psychogeology. The span of so many years creates a kind of temporal foreshortening in our minds; but at the time these things happened, the present was passing at the same speed as our present. It’s a long time. Mountains grow at about the same speed as your fingernails.

Mountain ranges far older than the Himalayas, Sierras, and Alps are still around, much worn down from their original size. They have sometimes broken up and drifted far from their original location. The Appalachians and the Scottish Highlands, for instance, are fragments of the same ancient mountain range. In another example, a mountain in Gondwana got split in two; now half of it is Table Mountain, overlooking Cape Town, South Africa, while the other half, Mount Wellington, overlooks Hobart, Tasmania. It’s hard to imagine such lengths of time, such anchorless wandering of the landscape. Possibly it’s completely beyond us. It’s one of the wonders of geology for sure. It’s also something that being in the mountains can give you a feeling for—intimations, like mental shivers, as you look at the bare bones of the Earth, newly exposed to the world—meaning around 20 million years ago.

So the Farallon Plate shoved under the North American Plate and dove into the mantle, where the leading edge melted, five to ten miles down. If that melted rock had risen to the surface while still melted, volcanoes would have resulted, and the emergent lava would have quickly cooled to become various kinds of volcanic rock. The Cascades are a volcanic range like that. It happens quite often.

In the Sierras, the Alps, and the Himalayas, the melted rock never made it to the surface. It pushed up against the rock over it, but that roof held, so the melted rock slowly cooled down there. That deep slow cooling of melted crustal rock creates granite; and a big mass of granite is called a batholith.

The Sierra Nevada batholith emerged into the light of day only after the vertical miles of Earth over it eroded away. Now it extends from a bit north of Lake Tahoe to Tehachapi Pass in the south. If you could see the whole batholith free and clear in the air, it would be shaped something like a backpacker’s air mattress: 450 miles long, 60 miles wide, and, because it still extends about six miles deep into the earth, while standing two to three miles above the land surrounding it, about eight or nine miles thick.

None of this was a uniform process. The batholith never looked exactly like an air mattress down there; it was maybe more like a band of cumulus clouds, with individual blobs of melted rock mashed together at their edges. Those individual blobs are called plutons. They’re lumped together like party balloons, or the bumpy top of a parasail. That’s the range as we see it: the slightly rounded tops of about 20 oval blobs, all pressed together. They’re often oval rather than circular, averaging around 10 miles by 20 in size.

The rock is a bit different chemically from blob to blob. Granite is a mix of minerals, with silica composing 60 to 80 percent of the mass. Silica is the whitish part of granite, and the black flecks are mostly feldspar and hornblende; there’s also often a reddish dash of iron oxide, and crystals of quartz. The slower the rock cooled, the more time there was for quartz crystals to grow. Taken all together, this mineral mixture makes a white or gray (or pinkish or orangish) speckled rock, its components present in differing proportions, such that many geologists don’t even use the word granite, except to refer to a family of rocks, or to make a concession to the common language of non-geologists.

I call it granite.

The pluton called the Whitney Intrusive Suite is one of the biggest and youngest in the Sierra. Being large, it took longer to cool, which allowed bigger-than-usual crystals of potassium feldspar to grow. These crystals are called phenocrysts: you can see them as the large cube shapes that stud many boulders in the area. “It is as if the rock itself is hobnailed,” as Kenneth Rexroth once said.

The Whitney granite is between 69 and 73 percent silica; there are whiter granites farther north, as in the Cartridge pluton. The Cartridge pluton, as seen from Pinchot Pass, is one of the most visible examples of an individual pluton that I know.

Since the plutons were emplaced, the miles of rock over them got slowly worn away by glaciers, rain, stream action, freeze-thaw cycles, wind, and sunlight. Slowly the batholith got closer to the Earth’s surface, and as the weight of the overburden on it grew less, the rock in the plutons expanded a little, thus causing them to crack in something like onion layers.

Eventually the batholith was exposed to the surface. There must have come a day when granite first peeked out of some broken metamorphic rock and looked up at the sky. The metamorphic roof continued to erode; a lot of it ran west into the Pacific, or filled California’s Central Valley, which is a big V-fold in the subducting plate, a bathtub trench eight miles deep, now filled with the rock that used to overlay the batholith.

So the granite mass rose, the east side of it more than the west, helping to give the Sierra its characteristic lifted-trapdoor appearance: long gentle rise on the west side (200 feet per mile, for 80 miles), sharp drop on the east side (1,000 feet per mile, for ten miles). Finally it burst into the open air, and kept lifting. It’s been rising from Cretaceous times until now, and the speed of its rise seems to be accelerating. The overall rise has been something between four and nine miles. It’s rising about one foot every thousand years.

Not the eternal hills, then. But eternal enough for us.

MY SIERRA LIFE (2)

Break On Through

About a hundred yards up the trail from the parking lot at Emerald Bay on Lake Tahoe, Terry stopped Joe and me, hand out like a traffic cop, blue eyes sparkling with pleasure. A fine morning. “Boys it’s time to drop.”

Happily we agreed and he handed us little squares of blue construction paper soaked in LSD. We ate the little scraps and continued up the trail. Thus began my first day in the Sierra Nevada.

Naturally this brings up some questions. Did taking LSD affect my first day in the Sierra Nevada? No doubt about it. Sometimes I’ve joked that I got high in the mountains that day and never came down, not from then till now. And it’s true! But not exactly.

It definitely made for a cosmic day, as we used to say. Hilarity often overcame us, as it did quite a lot in those days, whether we were on drugs or not; we liked to laugh, and the world struck us as funny. But what struck me most that day, and has lingered since in me, was a stupendous sensation of significance. This was not just me encountering the real world at last, which as a child of the suburbs was certainly part of it—it was more than that. It seemed to me that this mountain range I found myself in was more than real. I didn’t know what I meant by that, and I still don’t. Surreal is suggestive, given its etymology, but not right. Neither is spiritual, or mystical, or metaphysical, or existential, though all these words reach for the feeling. Naturally the ineffable and the inexpressible are also appropriate, given the elusiveness of the feeling, or its inexpressibility. I keep coming back to my original formulation: what I was seeing was more than real. That’s the feeling that stuck with me, and has never gone away. More real than real—the real reality—something like that.