The Romance of the Colorado River by Frederick Samuel Dellenbaugh
page 47 of 302 (15%)
page 47 of 302 (15%)
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when these deep-cut tributary canyons carried perennial streams, and
when the volume of the Colorado itself was many times greater, possessing a multiplied corrasive power, while the adjacent areas were about as arid as now. At such a time, perhaps, the Colorado performed the main work of the inner gorge, the Kanab, and similar affluents, their deep now rather evenly graded canyons. Such an increase of volume, if we suppose the aridity to remain as now, could have come about only by an increase of precipitation on the mountain summits. During the Glacial Epoch, the Rocky Mountain summits were considerably glaciated, the amount varying according to altitude and latitude. The general topography of the Colorado River was about as it is to-day, and the rainfall in the valleys probably nearly the same, or at least only a little greater. In other words, the conditions were those of to-day intensified. In summer, then, the amount of water seeking outlet by these drainage channels to the sea was enormously multiplied, and the corrasive power was correspondingly augmented. When the ice caps finally began to permanently diminish, the summer floods were doubtless terrific. The waters of the Colorado now rise in the Grand Canyon, on the melting of the snows in the distant mountains, from forty to one hundred feet; the rise must then have amounted to from one hundred to four hundred or more. The Kanab heads in two very high regions--the Pink Cliffs and the Kaibab. Though probably not high enough to be heavily glaciated they were high enough to receive an increased snowfall and to hold it, or a portion of it, over from one year to another. Thus the canyons having their origin on these high regions would be given perennial streams, with torrential floods each summer, compared with which anything that now comes down the Kanab would be a mere rivulet. The summit of the Kaibab is covered with peculiar pocket-like basins having no apparent outlets. These were possibly glacial sinks, |
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