Geology of the Great Basin

1. Introduction

1 introduction The dry sand stretches away as far as I can see to the east and the west. The July sun burns a hole in the sky and sears the desert basin. Shimmering heat waves ripple the sand at the horizon and make the reflections of the mountains flicker upside down on the pseudoliquid surface. The sandy mud has shrunk and cracked since the last summer rain and has formed polygonal fractures in the barren brown surface. These are the only marks on the sand. One hundred years ago, feet and ironbound wooden wheels churned the dust of this desolate sandy valley. Emigrants, bound for Oregon, took a shortcut across this forsaken stretch. It was a dash across the sand before the sun parched their tongues black with thirst and shriveled the stock to walking skeletons, or before the sky blackened with the rare but fatal summer rain that would flood the dust-covered basin with water and turn the silts to viscous mud. With wagons mired up to their axles, the emigrants foundered in a sea of muck. Here, in the Black Rock Desert of what would become northern Nevada, the emigrants would watch for a large dark knob across the shimmering sands and beeline straight for it. Below this black rock and slightly to the north is Double Hot Springs. Here the parched people and stock would find boiling hot water, confirming the devil’s role in fashioning this land. Downstream , where the water had cooled sufficiently to allow the growth of thick mats of grass, they found respite from the drought lands. This is an unforgiving land, a land of rapid change and contrast. This is the Great Basin of the American desert. What geologic forces created this mountain-studded sandand sage-filled bowl? 4 Introduction Curious, I visited the emigrants’ landmark. Turning the black rocks over in my hand, I marveled at the shiny crystalline texture. The rock is an exotic. A foreigner. It is not a resident of the original North American continent but a piece of another land that crushed against the western edge of the continent several hundred million years ago. The emigrants were orienting their journey by another emigrant. I pondered the irony. How do we know the black rock is not a part of our continent? If pieces of crust move, what propels them? Are their motions controlled by fundamental laws of physics, or do they move in a random fashion? I felt like a cerebral emigrant venturing timidly into the unknown of an abysmally deep past. Miles away, I stood atop the crags that crown a desert mountain range. The cold wind tousled my hair and gently nudged my body toward the cliff edge. Mountains. Through squinted, windburned eyes washed with tears, all I could see were mountains. Great walls of mountains leaned against the horizon like serrated stage sets. They tilted in ordered ranks above the sagegreen valleys, essentially north-south, hundreds of miles long. Shuddered by earthquakes and punctured by volcanoes, the ranges stand like ships lying at anchor before a steady north wind. Why? In the middle of the sagebrush desolation, in the central part of a valley surrounded by snowcapped mountains, steam rose above the winter-browned grasses. In the desert, where water is the most precious and scarce resource, I lay in hot water up to my neck. And I had a choice of not one pool but many. This area was named Thousand Springs, but I would wager they have never been counted. “Water, water everywhere,” here in a land of scarcity. Why? Sand makes a terrible bed. Its apparent stability is a well-known illusion, and I should have known better. Once again I shake the grains from my bedroll as I have at Jarbidge and Cathedral canyons and in valleys called Death and Fire. I have tidied my bedroll in countless other canyons, valleys, and ranges, many without names. If one is to study sand, one must learn to live with it. I am a geologist, and to study the earth I must accept a little grit with the grain. For thirty years I have had an intimate relationship with the earth. We’ve had our quarrels, inconsequential like the sand grains or more serious when a cliff face collapses. But these are lovers’ squabbles and of little import. We share secrets. Rambling throughout desert lands, poking in hidden recesses, struggling on glacial ice, diving into lakes and ocean, floating in...