The Coast Ranges

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In this cross section, the Coast Ranges occupy forty miles, the valley fifty miles, the mountains ninety. All of it added together is not a great distance. It is not as much as New York to Boston. It is Harrisburg to Pittsburgh. In breadth and in profile, a comparable country lies between Genoa and Zurich-the Apennines, the Po Plain, the Alps. An old VW bus is best off climbing the Sierra from the west. Often likened to a raised trapdoor, the Sierra has a long and planar western slope and-near the state line-a plunging escarpment facing east. The shape of the Sierra is also like an airfoil, or a woodshed, with its long sloping back and its sheer front. The nineteenth-century geologist Clarence King compared it to “a sea-wave” -a crested ocean roller about to break upon Nevada. The image of the trapdoor best serves the tectonics. Hinged somewhere beneath the Great Valley, and sharply faulted on zakelijke energie vergelijken its eastern face, the range began to rise only a very short geologic time ago-perhaps three million years, or four million years-and it is still rising, still active, continually at play with the Richter scale and occasionally driven by great earthquakes (Owens Valley, i872). In geologic ages just before the uplift, volcanic andesite flows spread themselves over the terrain like butterscotch syrup over ice cream. Successive andesite flows filled in local landscapes and hardened flat upon them. As the trapdoor rises-as this immense crustal block, the Sierra Nevada, tilts upward-the andesite flows tilt with it, and to see them now in the roadcuts of the interstate is to see the angle of the uplift. Bear in mind how young all this is. Until the latter part of the present geologic era, there was no Sierra Nevada-no mountain range, no rain shadow, no ten-thousand-foot wall. Big rivers ran west through the space now filled by the mountains. They crossed a plain to the ocean. Remember about mountains: what they are made of is not what made them. With the exception of volcanoes, when mountains rise, as a result of some tectonic force, they consist of what happened to be there. If bands of phyllites and folded metasediments happen zakelijke energie to be there, up they go as part of the mountains. If serpentinized peridotites and gold-bearing gravels happen to be there, up they go as part of the mountains.