Part 20 (1/2)

If this cannot be done, a narrow place in the canon of the stream is selected, above which there is a broad valley. At such a place the dam which is built across the canon is held firmly in place by the walls of rock upon each side, and an artificial lake or reservoir is made. Ditches lead away from this reservoir, and by means of gates the water is supplied when and where it is needed.

[Ill.u.s.tration: FIG. 116.--SWEEt.w.a.tER RESERVOIR, NEAR SAN DIEGO, CALIFORNIA]

The streams which furnish the water for irrigation in the arid region rise in mountains with steep rocky slopes, and until the water issues from these mountains it is confined to canons with bottoms of solid rock, so that no water is lost except by evaporation.

After the streams emerge from the canons upon the long, gentle slopes of gravel and soil which lie all about the bases of the mountains, they begin immediately to sink into the porous material.

They frequently disappear entirely before they have flowed many miles. Some of this water can be brought to the surface again by digging wells and constructing pumping plants, but the greater part is lost to the thirsty land.

To prevent the water from sinking into the gravel, ditches lined with cement are often made to carry it from the canons to the points where it is needed. Sometimes iron pipes or wooden flumes are used in place of the ditches.

What a transformation irrigation makes in the dry and desert-like valleys of the West! Land which under Nature's treatment supports only a scanty growth of sagebrush or greasewood, and over which a few half-starved cattle have roamed, becomes, when irrigated, covered with green fields and neat homes, while sleek, well-fed herds graze upon the rich alfalfa. Ten acres of irrigated land will in many places support a family, where without irrigation a square mile would not have sufficed.

One might suppose that the soil of these naturally barren valleys was poor, but such is not the case. The ground did not lack plant food, but merely the water to make this food available. With plenty of water the most luxuriant vegetation is produced. The soil is, indeed, frequently richer than in well-watered regions, for a lavish supply of water carries away a portion of the plant food.

In some places, where the land is almost level and the soil is filled with large quant.i.ties of soluble materials, such as soda and salt, keeping the ground moist through irrigation brings these substances to the surface in such quant.i.ties as to injure and sometimes kill the vegetation. In order that such lands may be successfully cultivated, the salts have to be either neutralized or washed away.

[Ill.u.s.tration: FIG. 117.--IRRIGATING DITCH, NEAR PHOENIX, ARIZONA]

Many of the rivers of the West carry large quant.i.ties of silt in suspension, which fills the ditches and causes a great deal of trouble; but when the silt is deposited over the surface it adds continually to the richness of the land.

The full development of irrigation will mean a great increase in the population and wealth of all the Western States.

THE LOCATION OF THE CITIES OF THE PACIFIC SLOPE

This old earth has to be consulted upon every occasion. It is a silent partner in all our undertakings. We sometimes think that we come and go as we please, but a little thought convinces us that we are not really so free.

The traveller must take account of the slopes of the land. It is much easier for him to follow a valley and cross a mountain range through a low spot, although his course be very crooked, than it is to make a ”bee line” for his destination. The farmer, in choosing his home and the kind of produce which he will raise, has to consult the soil and climate. He cannot expect to grow grain where the soil is poor and dry, or grow apples where the late spring frosts kill the buds. The miner knows that he cannot expect to find gold veins in the valleys, where the rocks are deeply covered by the soil, and so he turns his steps toward the mountains, where Nature has made his work easy by lifting up the rocks and exposing them to his view.

Routes of commerce and trade are governed by geographic, and to a certain extent by climatic, conditions. Shallow streams with rapids and waterfalls obstruct navigation. The absence of harbors along a given coast makes it difficult for s.h.i.+ps to take and discharge cargoes. Railroads cannot be constructed unless long and expensive surveys have first been made to determine the route which Nature has made the easiest between two given points.

The character of the climate and geographic features of a given country determine whether it shall become noted for agricultural productions, mining industries, manufactures, or commerce. The locations of the cities and towns and the roads connecting them depend upon geographic conditions. There is not an occupation of any importance in which people engage at any particular place that is not dependent in large degree for its success upon the conditions which Nature has imposed upon that place.

A city will not grow up at a given point unless the geographic conditions are favorable. There must be some natural reason to induce people to gather in large numbers in one place. At one spot there are facilities for manufacturing, such as water-power and coal, and easy means of communication with other parts of the world. At another, the only reason for the growth of a city is the existence of rich mines. A third place may be conveniently located in the midst of a rich agricultural region, where it is easy to bring in supplies and s.h.i.+p out the products of the soil.

A study of the founding and growth of some of the cities of the West, and particularly of the Pacific slope, will bring out many interesting facts.

San Francisco is the metropolis of the Pacific; its population will soon reach half a million. If we look back seventy-five years we find San Francisco an unimportant Mexican military post and the seat of one of the smaller missions. Monterey, the capital of the province of California and one of the two leading towns (Los Angeles being the other), apparently had all the advantages in the race for supremacy.

In date of discovery (1603) Monterey Bay has the advantage of more than one hundred and fifty years over San Francis...o...b..y. It is difficult to understand why the different navigators who sailed north along the coast failed to discover California's most magnificent bay. Sir Francis Drake went by it, evidently not seeing the narrow opening between the headlands now known as the Golden Gate. Vizcaino, after discovering Monterey Bay, also pa.s.sed by and anch.o.r.ed where Drake had stopped, in a little bay now called Drake's Bay, a few miles north of San Francis...o...b..y.

After the founding of San Diego, in 1769, a party started overland for Monterey, but by reason of the peculiar position of the bay they pa.s.sed it unknowingly, and by accident came upon the body of water which has since been of so great importance to the commercial life of California. Monterey Bay in time lost its importance, partly because it was not thoroughly protected from the storms, and partly from the lack of easy communication with the rest of the state.

Immediately after the acquisition of California and the discovery of gold, the advantages of San Francis...o...b..y began to be appreciated, and the little Mexican town grew rapidly. The narrow entrance to the bay, which had for so long a time delayed its discovery, completely protected it from the storms, while its long arms opened across the coast mountains directly into the important valleys of the interior. Ocean vessels could go up the bay and through the Strait of Carquinez, while river boats could be used for many miles farther.

After the discovery of gold, s.h.i.+ps from all parts of the world found ample room and shelter in San Francis...o...b..y; and the incoming miners, going by the water routes to Marysville, Sacramento, and Stockton, easily reached the gold-bearing gravels of the Sierra Nevada streams.

With the exception of southern California and a portion of the northern coast, almost all the agricultural and mineral resources of California are directly tributary to San Francisco. This place is naturally the centre of home trade, of foreign commerce, and of population.

[Ill.u.s.tration: FIG. 118.--SAN FRANCIs...o...b..Y

Formed by the sinking of the land and flooding of a river valley]

Nature failed to supply San Francisco with one essential advantage, namely, cheap power for manufacturing. There is no water-power near and but little coal in the state. Since the coal has to be s.h.i.+pped in from distant points, its high price has impeded manufacturing. But now it appears that San Francisco is not so badly off after all, for important deposits of petroleum have been discovered in the central and southern portions of California; and besides, processes have been invented for transforming the unlimited water-power of the mountain streams into electric energy, and transmitting this power to all the cities about the bay.