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 quantities of soluble materials, such as soda and salt, keeping the ground moist through irrigation brings these substances to the surface in such quantities 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. [Illustration: FIG. 117.--IRRIGATING DITCH, NEAR PHOENIX, ARIZONA] Many of the rivers of the West carry large quantities 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.