DESERT TIME -- A JOURNEY THROUGH THE AMERICAN SOUTHWEST
Chapter 25: strata
Dinted, cleaved, scarred with white, the cobbles lie in the high light and dust, as if someone had scooped truckloads of riverbed and run it through a damaging machine: the turbine blades of a jet engine, say. Before this damage the cobbles were almost perfectly oval, rounded by years of swiftly running water. Here and now the sound of that comes back: the gutteral clonking of a river rising over its banks, in flood, its water gone the color of milky tea.
Cobbles like these are what you see sorted into curves, according to weight, up on drying banks later in the year. Even shattered as they are and bunged up and wholly out of place they are river cobbles still. They are all colors; deep green, maroon, silver, gray, old-mustard yellow; they came from all over, washed downstream in ecumenical mix. As we go on around the shoulders of the range more of them appear, layers and lenses of cobbles line the road cuts and the walls of the canyons. They came swept down in tributaries over years. The deposits are massive: there was a big river here for a long time.
Now this is the dry northern buttress of the Amargosa Range known as the Grapevine Mountains, a worn multicolored fault block that forms the northeastern rim of Death Valley. From a distance one sees that these mountains are streaked with red and dark and pale like thick sliced bacon or badly carved layer cake, each layer and streak being a stratum, like a book page in the montane tome. Many of these strata are made of river cobbles. Like pages of translations, these came from somewhere else.
Here the earth is straining as you sit, like teeth bearing down on a bullet. The crust of the continent has cracked wholly through in more or less parallel lines, the side chunks thrusting up and the center chunk dropping away between them, thirty thousand some feet away -- nearly six miles -- filling as it goes with water and mountain debris but dropping (still dropping, now, tilting east as it sinks) faster than anything nowadays can fill it up. That isn't, really, Death Valley out there. "Valley" to a geologist means something that water has worn into being, or glacial ice, that being water of a kind. A dropped slab between thrusted mountains is known as a graben, suggesting that it has been grabbed onto and is being hauled to Hell by demon gravity.
The graben's bordering chunks have been shoved up, in a kind of bobbing motion, as the graben drops into the semifluid hot rocks of earth's upper mantle. These bordering chunks are now mountains: the Amargosas and the Panamints, respectively. Grapevine Mountain with all its cobble strata is well over eight thousand feet up, right now, but has been crumbling as it has been thrusting all the time, so who knows where it would be were it still whole; and who knows what "whole" is, or was, flux being constant in the world, as the cobbles bear witness. In all this hashing of bedrock it's no wonder that the river has vanished from what are now these mountaintops. Were there water enough to feed it, it would not run here.
Telescope Peak in the Panamint Range, on the far side of the Death Valley graben, is more than eleven thousand feet above sea level and is covered with snow. Through binoculars it looks moonlit; the iced slopes are specked with fir trees, linear and dark.
The graben itself has gone below what we're used to as being possibility. Much of its heartland is below sea level and some of it lies two hundred and eighty-two feet under the surface of theoretical waves. It also looks moonlit, dry and long and white, as if the planet itself had run through a damaging machine and been left with this gash, scarred with salt.
We start down from the Grapevine highlands by following the cleft of a wash. The wash drops between worn walls and narrows and its pitch steepens as we go: what is now Titus Canyon goes into Death Valley like a bobsled run.
All the way down I notice that wash and canyon are floored with cobbles. Some of them are the old ones washed from their strata and loose again in what is, sometimes, the bed of a flash-flood river. Where the canyon ends, cobbles and other debris spread like a fan.
This fan is a phenomenon. Fans like this one form in deserts, and only in deserts. Where there is more water in the world there are perennial streams that carry their load on down and on down; they deposit their debris in wide-bosomed floodplains or, at the end, in deltas. A delta forms at river's end. Here, all rivers end at the mouths of their canyons. There, the water simply ... sinks. The waterborne debris is dropped as if from the tailgate of a dump truck: in a fan.
One trundles down this fan out into the pale floor of Death Valley.
This is the shape of the country. One sees right away that there are two kinds of ground here: bedrock and alluvium. Alluvium is bedrock that has been torn and worn away and is loose and trending downhill: everything, that is, from boulders to salts. The canyons and washes are strewn with loose gravels; where canyons enter the graben lie the alluvial fans; the graben is floored with level layers of sand, silt, and evaporites: borax, salt.
Bedrock, alluvium. The terms are relative. As the cobbles make clear, most bedrock strata were alluvium, once.
We woke in Death Valley this morning with mountains all around us in clean silhouette, well before dawn, on a bright planet that was as clean-featured as the moon. Close by there were neatly spaced silhouettes of creosote bush, sketches of branches as thin and tough as tungsten wire. Then the rurk of a raven and the black bird's deliberate passage across the stars. Then red light crept down bedrock peaks and alluvial skirts, the sky was turquoise, the clumps of bursage silver. We saw that there were tracks of crickets and kangaroo mice in the sand and a few darkling beetles trundling. Otherwise there was nothing to see but rock.
This is what there is to see: rock. Here there are countless geodramas written in fault block rising and fault block dropping down, in spews of volcanic ash the colors of muddy indigo, mustard, and peach.
Plate tectonics may be the power here, but the driest piece of this continent has been designed by water. In spite of the fact that the rainfall averages an inch and a half a year, water has carved cobbles, has ground sand, has routed out canyons, is the weaver of alluvium, is the tireless carrier of silts and dissolver of salts. It is the maker of landscape. The absent maker, like God.