The Western United States | Page 3

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.
[Illustration: 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, 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