EASTERN END (DESERT VIEW, CAPE ROYAL). THE FLOOR OF THE CANYON IS HERE FORMED OF TILTED ROCKS OF THE SECOND ERA. THE UPPER WALLS ARE OF COMPARATIVELY HORIZONTAL ROCKS OF THE THIRD ERA.
THE GRAND CANYON
Those who have been to the rocky shores of the Colorado River in Grand Canyon, who have heard its wild roar, and seen its mad waves rush along their course, need no further introduction to the power of this stream. It is a mighty river! In the open stretch above the mouth of Bright Angel Creek its speed varies between two and a half and ten miles an hour. Its width at the same place is over one hundred yards and its depth between twelve and forty-five feet. But the Colorado River alone would have made but little progress were it not for the many rocks—boulders, pebbles, and sand grains—all of which act as tools and are constantly gouging and cutting as they move. Just as sandpaper rubbing over the same place continuously leaves its groove, so this combination of power and tools is ever carving its course. The Colorado River during a vast period has cut almost a mile vertically through all of the great rock layers now exposed in the walls of Grand Canyon.
The width of the Grand Canyon, an average of about ten miles, has been brought about by the wearing and washing-in of its sides by natural processes of erosion. Rain, wind, frost, temperature changes and plant action have all combined to break down the Canyon walls. The soft rocks on the slopes are continually being broken and removed; the more resistant ones in the cliffs are undermined so in time fall down. While the river has been cutting deeper, the Canyon’s sides have been steadily receding. The Grand Canyon itself is the valley of the Colorado, and its narrowness rather than its width is the remarkable feature when compared with the valleys of other rivers. This present canyon profile has been brought about as the combined effects of an arid climate and a rapidly downward cutting river.
Even a distant view of the Colorado River in the Grand Canyon bottom is sufficient to convince one of the tremendous transporting power of this stream. Thus it not only does the work of cutting downward, but also carries off the vast load of sand and silt which is continually emptied into its waters. It has been aptly described as being “too thick to drink but too thin to plow.” In this region the river known at its headwaters as the “Silvery Colorado” bears even a higher percentage of sediment than does the muddy Mississippi-Missouri. It has been found from carefully made tests by the United States Geological Survey that the Colorado River carries past any given point in the Grand Canyon an average of nearly a million tons of sand and silt every day. Thus has the Grand Canyon been excavated!
THE FORMING OF ZION CANYON
(PLIOCENE AND PLEISTOCENE EPOCHS)
“A Yosemite Valley in colors” is a very apt description which has often been applied to Zion Canyon in southern Utah. Sheer-walled with a beautiful flat valley floor, this canyon is not unlike California’s glacier-carved fairyland in general size and shape, but in formation it has a very different history.
