Part 1 (2/2)
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.
[Ill.u.s.tration: FIG. 2.--LOOKING DOWN THE COLORADO RIVER FROM ABOVE THE NEEDLES]
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 pa.s.ses, 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 canons. 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 gla.s.sful 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 gla.s.s was six inches deep, there will finally remain in the bottom a ma.s.s 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.
[Ill.u.s.tration: FIG. 3.--LOOKING TOWARD THE DELTA OF THE COLORADO FROM YUMA]
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, r.e.t.a.r.ding 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 sh.o.r.e. 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 sh.o.r.es of this old lake, and on them are found the pearly sh.e.l.ls of mult.i.tudes of fresh-water mollusks. The presence of these sh.e.l.ls 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. Ca.n.a.ls 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 canons 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 canons will be carried away in the form of sand and mud. Broad valleys will replace the canons, 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.
A TRIP INTO THE GRAND CAnON OF THE COLORADO
We may read of the Colorado plateau, and of the Grand Canon with its precipitous walls of variously colored rock, but unless we actually visit this wonderland, it is hard to realize the height and extent of the plateau and the depth of the gashes made in its surface by running water, gashes so deep that they seem to expose the very heart of the earth.
Nature has chosen a remote and half-desert region for the location of this, the most picturesque canon in the world, as if she wished to keep it as long as possible from the eyes of men. Once a traveller could not view the canon without making a long and weary journey across hundreds of miles of desert; now it is quite different, for one can almost look into its depths from the windows of a palace car. But to appreciate and understand fully the stupendous work that nature has done throughout this region we must leave the cars at a somewhat distant point, and before reaching the canon become acquainted with the country in which it lies through the old-fas.h.i.+oned ways of travelling on horseback or wagon.
Flagstaff was formerly the starting-point for travellers to the canon, and we will choose it now, for the old stage road offers an interesting ride. The road first winds around that lofty snow-clad peak, the San Francisco Mountain, which can be seen from all northern Arizona. Leaving the mountain behind, we strike out directly across the high plateau. The country is nearly level, and the open park-like forest extends in every direction as far as one can see.
It is difficult for us to believe that we are seven thousand feet above the sea, a height greater than that of the highest mountains in the United States east of the Mississippi Valley. It is this elevation, however, which brings the summer showers and makes the air cool and pleasant, for the lowlands of this portion of the United States are barren deserts, upon which the sun beats with almost savage heat.
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