Back Aa

Western United States, The

<h2>THE WORK OF THE COLORADO RIVER</h2> The Colorado River is not old, as we estimate the age of rivers. It was born when the Rocky Mountains were first uplifted to the sky, when their lofty peaks, collecting the moisture of the storms, sent streams dashing down to the plains below. Upon the western slope of the mountains a number of these streams united in one great river, which wound here and there, seeking the easiest route across the plateau to the Gulf of California. At first the banks of the river were low, and its course was easily turned one way or another. From the base of the mountains to the level of the ocean there is a fall of more than a mile, so that the river ran swiftly and was not long in making for itself a definite channel. Many thousands of years passed. America was discovered. The Spaniards conquered Mexico and sent expeditions northward in search of the cities of Cibola, where it was said that gold and silver were abundant. One of these parties is reported to have reached a mighty cañon, into which it was impossible to descend. The cañon was so deep that rocks standing in the bottom, which were in reality higher than the Seville cathedral, appeared no taller than a man. Another party discovered the mouth of the river and called it, because of their safe arrival, The River of Our Lady of Safe Conduct. They went as far up the river as its shallow waters would permit, but failed to find the seven cities of which they were in search, and turned about and went back to Mexico. For years afterward the river remained undisturbed, so far as white men were concerned. A great part of the stream was unknown even to the Indians, for the barren plateaus upon either side offered no inducements to approach. Trappers and explorers in the Rocky Mountains reached the head waters of the river nearly one hundred years ago, and followed the converging branches down as far as they dared toward the dark and forbidding cañons. It was believed that no boat could pass through the cañons, and that once launched upon those turbid waters, the adventurer would never be able to return. The Colorado remained a river of mystery for nearly three centuries after its discovery. When California and New Mexico had become a part of the Union, about the middle of the last century, the cañon of the Colorado was approached at various points by government exploring parties, which brought back more definite reports concerning the rugged gorge through which the river flows. In 1869 Major Powell, at the head of a small party, undertook the dangerous trip through the cañon by boat. After enduring great hardships for a number of weeks, the party succeeded in reaching the lower end of the cañon. Major Powell's exploit has been repeated by only one other company, and some members of this party perished before the dangerous feat was accomplished. <div class="img_ctr" style="width: 713px;"> <ANTIMG src="images/fig001.jpg" width-obs="713" height-obs="481" alt="Fig. 1"> FIG. 1.—THE GRAND CAÑON OF THE COLORADO The work of a river </div> The Colorado is a wonderful stream. It is fed by the perpetual snows of the Rocky Mountains. For some distance the tributary streams flow through fertile valleys, many of them now richly and widely cultivated. But soon the branches unite in one mighty river which, seeming to shun life and sunlight, buries itself so deeply in the great plateau that the traveller through this region may perish in sight of its waters without being able to descend far enough to reach them. After passing through one hundred miles of cañon, the river emerges upon a desert region, where the rainfall is so slight that curious and unusual forms of plants and animals have been developed, forms which are adapted to withstand the almost perpetual sunshine and scorching heat of summer. Below the Grand Cañon the river traverses an open valley, where the bottom lands support a few Indians who raise corn, squashes, and other vegetables. At the Needles the river is hidden for a short time within cañon walls, but beyond Yuma the valley widens, and the stream enters upon vast plains over which it flows to its mouth in the Gulf of California. No portion of the river is well adapted to navigation. Below the cañon the channels are shallow and ever changing. At the mouth, enormous tides sweep with swift currents over the shallows and produce foam-decked waves known as the "bore." Visit the Colorado River whenever you will, at flood time in early summer, or in the fall and winter when the waters are lowest, you will always find it deeply discolored. The name "Colorado" signifies red, and was given to the river by the Spaniards. Watch the current and note how it boils and seethes. It seems to be thick with mud. The bars are almost of the same color as the water and are continually changing. Here a low alluvial bank is being washed away, there a broad flat is forming. With the exception of the Rio Grande in New Mexico, and the Gila, which joins the Colorado at Yuma, no other river is known to be so laden with silt. No other river is so rapidly removing the highlands through which it flows. <div class="img_ctr" style="width: 513px;"> <ANTIMG src="images/fig002.jpg" width-obs="513" height-obs="352" alt="Fig. 2"> FIG. 2.—LOOKING DOWN THE COLORADO RIVER FROM ABOVE THE NEEDLES</div> Over a large portion of the watershed of the Colorado the rainfall is light. This fact might lead one to think that upon its slopes the work of erosion would go on more slowly than where the rainfall is heavy. This would, however, be a wrong conclusion, for in places where there is a great deal of rain the ground becomes covered with a thick growth of vegetation which holds the soil and broken rock fragments and keeps them from being carried away. The surface of the plateaus and lower mountain slopes in the basin of the Colorado are but little protected by vegetation. When the rain does fall in this arid region, it often comes with great violence. The barren mountain sides are quickly covered with trickling streams, which unite in muddy torrents in the gulches, carrying along mud, sand, and even boulders in their rapid course; the torrents in turn deliver a large part of their loads to the river. As the rain passes, the gulches become dry and remain so until another storm visits the region. It is storming somewhere within the basin of the Colorado much of the time, for the river drains two hundred and twenty-three thousand square miles. So it comes about that whether one visits the river in winter or summer one always finds it loaded with mud. But what becomes of all this mud? The river cannot drop it in the narrow cañons. It is not until the river has carried its load of mud down to the region about its mouth, where the current becomes sluggish, that the heavy brown burden can be discharged. Dip up a glassful of the water near the mouth of the river, and let it settle, then carefully remove the clear water and allow the sediment in the bottom to dry. If the water in the glass was six inches deep, there will finally remain in the bottom a mass of hardened mud, which will vary in amount with the time of the year in which the experiment is performed, but will average about one-fiftieth of an inch in thickness. Each cubic foot of the water, then, must contain nearly six cubic inches of solid sediment or silt. It has been estimated that the average flow of the Colorado River at Yuma throughout the year is eighteen thousand cubic feet of water per second. From this fact we can calculate that there would be deposited at the mouth of the river every year, enough sediment to lie one foot deep over sixty-six square miles of territory. Nearly one three-hundredth part of the Colorado River water is silt, while in the case of the Mississippi the silt forms only one part in twenty-nine hundred. <div class="img_ctr" style="width: 514px;"> <ANTIMG src="images/fig003.jpg" width-obs="514" height-obs="340" alt="Fig. 3"> FIG. 3.—LOOKING TOWARD THE DELTA OF THE COLORADO FROM YUMA</div> Now we are prepared to understand the origin of the vast lowlands about the head of the Gulf of California. Long ago this gulf extended one hundred and fifty miles farther north than it does at present, so that it reached nearly to the place where the little town of Indio now stands in the northern end of the Colorado desert. When the Colorado River first began to flow, it emptied its waters into the gulf not far from the spot where Yuma is situated. The water was probably loaded with silt then as it is now. Part of this sediment was dropped at the mouth of the stream, while part was spread by the currents over the bottom of the adjoining portions of the gulf. The rapidly growing delta crept southward and westward into the gulf. As fast as the sediment was built up above the reach of the tide, vegetation appeared, which, retarding the flow of the water at times of flood, aided the deposition of silt and the building up of the delta. As the centuries went by, these lowland plains became more and more extensive, until the gulf was actually divided into two parts by the spreading of the delta across to the western shore. The portion of the gulf thus cut off from the ocean formed a salt lake fully one hundred miles in length. We may suppose that for a long time before the barrier was high and strong, the tidal currents occasionally broke over the delta and supplied the lake with water. As the river meandered here and there over the flat delta, its channels must have undergone many changes at every time of flood. A part of the water without doubt flowed into the salt lake, and another portion into the open gulf. In fact, the basin in which the lake lay, now known as the Colorado desert, continued to receive water from the river, at intervals, until very recently. In 1891 an overflow occurred, through the channel known as New River, which flooded the lower portion of the basin and threatened to cover the railroad. When the ocean had been permanently shut off from the head of the gulf, and the river itself had been largely diverted toward the south, the lake began to dry up. At last, most of the water disappeared and there remained a vast desert basin, at its greatest depth two hundred and fifty feet below the level of the ocean. In the bottom of the basin a bed of salt appeared, for this substance could not be carried away, as the water had been, by the thirsty air. Remarkably perfect beaches still exist around the shores of this old lake, and on them are found the pearly shells of multitudes of fresh-water mollusks. The presence of these shells leads us to believe that after the salt lake dried up, the river again broke in and formed a new lake of comparatively fresh water which also, after a time, dried up. The wonderful fertility of the Colorado delta is just beginning to be appreciated. Canals have been dug to take the water from the river and distribute it over the land. Year by year the cultivated lands are being extended. The change which irrigation is making upon the surface of one of the worst deserts in the country is indeed remarkable. The Colorado River is working on quietly and steadily. We may think, and truly, that it has already done a great at work in excavating the mighty cañons along its course, but, in reality, the work already accomplished is small in comparison with that which remains to be done. In time, if the land is not disturbed by the forces which build mountains, the plateaus through which the river now flows in such deep cañons will be carried away in the form of sand and mud. Broad valleys will replace the cañons, and the Gulf of California will become a fertile plain. As the highlands wear away the process will go on more and more slowly, for there will be less rainfall. The river will become smaller and its basin more arid. All these changes will be brought about through the crumbling of the rocks, and the removal of the waste matter by the running water. <div style="break-after:column;"></div>

1 of 2

2 of 2

Update Required To play the media you will need to either update your browser to a recent version or update your Flash plugin.