The most striking pediment

Gerelateerde afbeelding

Boulder beds in the roadcuts represented, as Love put it, “the deroofing of tl1e Medicine Bow Mountains in the first pulsation of the Laramide Revolution.” The beds were of Paleocene age. In a knife-edge ridge a few miles farther on, the interstate had exposed the same conglomerates tilted forty-five degrees as mountain building continued. And soon after that came a flat-lying Eocene deposit. “So you have a time frame for the orogeny,” Love said, and this was when he added, “It didn’t take very long for those mountains to come zakelijke energie up, to be deroofed, and to be thrust eastward. Then the motion stopped. That happened in maybe ten million years, and to a geologist that’s really fast.” Near Arlington, an anomalous piece of landscape reached straight out from the mountains like a causeway heading north. It was capped with stream gravel, brought off the mountains by furious rivers rushing through the tundras of Pleistocene time. The gravel had resisted subsequent erosion, while lighter stuff was washed away on either side. Geologists call such things pediments, and Love remarked that the one before us was “the most striking pediment in this region.” In my mind’s eye I could see the braided rivers coming off the Alaska Range, thickly spreading gravels, perhaps to preserve beneath them the scenes of former worlds. Where I-80 cut through the Arlington pediment, the zakelijke energie vergelijken Pleistocene gravel rested on Eocene sandstones, on red and green claystones; and they in turn covered conglomerates that came from the mountains when the mountains were new. One could read upward from one world to another: the boulders falling from rising mountains, the quiet landscapes after the violence stopped-all preserved in a perplexing memento from the climate of an age of ice. In a cut eight miles farther on, that early conglomerate was in contact with Cretaceous rock bent upward even more steeply as the Laramide Orogeny lifted the mountains. Picking through the evidence in the conglomerate was like sorting out debris from an explosion.