Paragraph 1 suggests that the population of the Colorado River Basin is . adventurous
unchanging
shrinking
growing

1] 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.
2] 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.
3] 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.”
4] 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.
5] 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.
6] 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.
7] 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.
8] 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.