Twenty thousand years

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This Eocene time line, drawn from either end of the continent, would have converged in western Wyoming in something comparable to the Sea of Azov. A hundred and fifty miles long, a hundred miles wide, it was larger by far than Erie, larger than Lake Tanganyika, larger than Great Bear. It was two hundred times Lake Maggiore. It had no name until a century ago, when a geologist called it Lake Gosiute. Lakes are so ephemeral that they are seldom developed in the geologic record. They are places where rivers bulge, as a temporary consequence of topography. Lakes fill in, drain themselves, or just evaporate and disappear. They don’t last. The Great Lakes are less than twenty thousand years old. The Great Salt Lake is less than twenty thousand years old. When Lake Gosiute took in the finishing touch of sediment that ended its life, it was eight million years old. West of Rock Springs, we came to an escarpment known as White Mountain, standing a thousand feet above the valley of Killpecker Creek. In no tectonic sense was this a true mountain-a folded-andfaulted, volcanic, or overthrust mountain. This was just a Catskill, a Pocono, a water-sliced segment of layered flat rock, a geological piece of cake. In fact, it was the bed of Lake Gosiute, and contained almost all of the eight million years. Apparently, the initial freshwater lake eventually shrank, became bitter and saline, and intermittently zakelijke energie may have gone dry. Later, as the climate remoistened, water again filled tl1e basin, and the lake reached its greatest size. As we looked at White Mountain, we could see these phases. It was the dry, salt-lake interval in the middle-straw and hay pastels so pale they were nearly white-that had given the bluff its name. The streams tl1at had opened it to view were lying at its base. Killpecker Creek (full of saltpeter) flowed into Bitter Creek, and that soon joined the Green River. Down the road a couple of miles was a pair of tunnels-snake eyes in the lakebed. They were one of the three sets of tunnels on Interstate So between New York and San Francisco, and they had to be there in the nose of White Mountain, or the interstate, flexing left, would destroy the town of Green River. Tower sandstone stood on the zakelijke energie vergelijken ridgeline in castellated buttes. With each mile, they increased in number, like buildings o”n the outskirts of a city. Off to the left was the island from which the geologist John Wesley Powell-seven years before the battle of the Little Bighorn-set off in a flotilla of dinghies to follow the Green River into its master stream, and to survive the preeminent rapids of North America on the first known voyage through the Grand Canyon. A huge sandstone broch stood in brown shale above the tunnels, which penetrated the lakebed’s saline phase.

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