Read Online Centennial by James A. Michener - Free Book Online Page A

had to be periods of long quiescence, but it does seem likely that some acted in concert, energized by a common agitation within the mantle. They deposited an incredible amount of new rock, more than fourteen thousand cubic miles of it in all.
    They glowed through the nights, illuminating in ghostly flashes the mountains and plains they were creating. At times they sponsored earthquakes, and then for some mysterious reason, possibly because the molten magma was exhausted, they died, one after another, until there were no active volcanoes in the region, only the clearly defined calderas which still stand to mark this age of violence.
    About fifteen million years ago the area underwent a massive dislocation in a process that extended for ten million years. The entire central portion of America experienced a massive uplifting. Perhaps the continental plate was undergoing some major adjustment, or there may have been a sizable disruption within the mantle. At any rate, the surfaces—both mountains and valleys to the west, and the low-lying flat plains to the east—rose. Colorado was uplifted to its present altitude. Rivers like the Missouri, which then ran north to the Arctic Ocean, began to take form, and the outlines of our continent assumed more or less their present shape. Many subsequent adjustments of a minor nature would still occur—for example, at this time North and South America were not yet joined—but the shapes we know were discernible.
    About one million years ago the Ice Age began to send its rapacious fingers down from the north polar ice cap. Because of intricate changes in climate, triggered perhaps by variations in the carbon dioxide content of the earth’s atmosphere or by accumulations of volcanic dust which intercepted the sun’s heat that otherwise would have reached the earth, large sheets of ice began to accumulate where none had been before.
    The glaciers invading North America reached so far south and were so thick, they imprisoned water that normally belonged to the oceans, which meant that shorelines which had lain submerged for the preceding millions of years now lay exposed. The great western glacier did not quite reach Centennial; it halted some distance to the north. But at high elevations in the Rockies, small glaciers did form and filled the valleys, and when they moved slowly to lower levels they gouged out the valley bottoms and carved the standing rocks, so that much of the beauty of the New Rockies stems from the work of the glaciers.
    They arrived in the mountains at spaced intervals, the first major one appearing about three million years ago; the last, only fifteen thousand years ago. But of course, at high, cold altitudes like the topmost New Rockies small glaciers persisted and still exist.
    As the mountain glaciers melted they produced unprecedented amounts of water, which created floods of gigantic proportion. They cascaded down with fierce velocity and submerged traditional rivers, causing them to expand many times their customary width. Much detritus was borne down from the mountains, most of it with sharp cutting edges, and it was this mixture of copious water and cutting rock which planed down the lands to the east.
    Sometimes, high in the Rockies, the glacier would impound a temporary rock-and-ice barrier, and behind it an enormous lake would be formed. It would exist for decades or centuries. Then, one day, there would be a violent cracking sound, and with one vast rush the contents of the lake would surge forth, miles wide until it roared into some confining canyon, when it would compress into a devastating liquid missile, shooting along with terrifying force, uprooting every living thing and ripping away huge boulders from the walls of the canyon before rushing at last onto the plains.
    There it would reach the river. A wall of water would fan out across the plains, engulfing both the river and its tributaries. Churning, roaring, twisting, it would scour everything