In general, the descent of the streams in the arid land is very great; for this reason the flood plains are small, that is, the extent of the lands adjacent to the streams which are subject to overflow at high water is limited. In general, these flood-plain lands should not be chosen for irrigation, from the fact that the irrigating canals are liable to be destroyed during flood seasons. Where the plan of irrigation includes the storage of the water of the non-growing season, by which all the waters of the year are held under control, the flood-plain lands can be used to advantage, from the fact that they lie in such a way as to be easily irrigated and their soils possess elements and conditions of great fertility.
Other locally controlling conditions are found in selecting the most advantageous sites for the necessary water works.
These are the chief physical factors which enter into the problem, and in general it will be solved by considering these factors only; but occasionally artificial conditions will control.
The mining industries of the Arid Region are proportionately greater than in the more humid country. Where valuable mines are discovered towns spring up in their immediate vicinity, and they must be served with water for domestic purposes and for garden culture. When possible, agriculture will be practiced in the immediate vicinity for the purpose of taking advantage of the local market. In like manner towns spring up along the railroads, and agriculture will be carried on in their vicinity. For this and like reasons the streams of the Arid Region will often be used on lands where they cannot be made the most available under physical conditions, and yet under such circumstances artificial conditions must prevail.
In the indication of specific areas as irrigable on the accompanying map of Utah, it must be considered that the selections made are but tentative; the areas chosen are supposed to be, under all the circumstances, the most available; but each community will settle this problem for itself, and the circumstances which will control any particular selection cannot be foretold. It is believed that the selections made will be advantageous to the settler, by giving him the opinions of men who have made the subject a study, and will save many mistakes.
The history of this subject in Utah is very instructive. The greater number of people in the territory who engage in agriculture are organized into ecclesiastical bodies, trying the experiment of communal institutions. In this way the communal towns are mobile. This mobility is increased by the fact that the towns are usually laid out on Government lands, and for a long time titles to the land in severalty are not obtained by the people. It has been the custom of the church to send a number of people, organized as a community, to a town site on some stream to be used in the cultivation of the lands, and rarely has the first selection made been final. Luxuriant vegetation has often tempted the settlers to select lands at too great an altitude, and many towns have been moved down stream. Sometimes selections have been made too far away from the sources of the streams, and to increase the supply of water, towns have been moved up stream. Sometimes lands of too great slope have been chosen, and here the waters have rapidly cut deep channels and destroyed the fields. Sometimes alkaline lands are selected and abandoned, and sometimes excessively sandy lands have caused a change to be made; but the question of the best sites for the construction of works for controlling and distributing the water has usually determined the selection of lands within restricted limits.
To a very slight extent indeed have artificial conditions controlled in Utah; the several problems have generally been solved by the consideration of physical facts.
INCREASE IN THE WATER SUPPLY.
Irrigation has been practiced in different portions of the Arid Region for the last twenty-five or thirty years, and the area cultivated by this means has been steadily increasing during that time. In California and New Mexico irrigation has been practiced to a limited extent for a much longer time at the several Catholic missions under the old Spanish regime. In the history of the settlement of the several districts an important fact has been uniformly observed—in the first years of settlement the streams have steadily increased in volume. This fact has been observed alike in California, Utah, Colorado, and wherever irrigation has been practiced. As the chief development of this industry has been within the last fifteen years, it has been a fact especially observed during that time. An increase in the water supply, so universal of late years, has led to many conjectures and hypotheses as to its origin. It has generally been supposed to result from increased rainfall, and this increased rainfall now from this, now from that, condition of affairs. Many have attributed the change to the laying of railroad tracks and construction of telegraph lines; others to the cultivation of the soil, and not a few to the interposition of Divine Providence in behalf of the Latter Day Saints.
If each physical cause was indeed a vera causa, their inability to produce the results is quite manifest. A single railroad line has been built across the Arid Region from east to west, and a short north and south line has been constructed in Colorado, another in Utah, and several in California. But an exceedingly small portion of the country where increase of water supply has been noticed has been reached by the railroads, and but a small fraction of one per cent. of the lands of the Arid Region have been redeemed by irrigation. This fully demonstrates their inadequacy. In what manner rainfall could be affected through the cultivation of the land, building of railroads, telegraph lines, etc., has not been shown. Of course such hypotheses obtain credence because of a lack of information relating to the laws which govern aqueous precipitation. The motions of the earth on its axis and about the sun; the unequal heating of the atmosphere, which decreases steadily from equator to poles; the great ocean currents and air currents; the distribution of land and water over the earth; the mountain systems—these are all grand conditions affecting the distribution of rainfall. Many minor conditions also prevail in topographic reliefs, and surfaces favorable to the absorption or reflection of the sun’s heat, etc., etc., affecting in a slight degree the general results. But the operations of man on the surface of the earth are so trivial that the conditions which they produce are of minute effect, and in presence of the grand effects of nature escape discernment. Thus the alleged causes for the increase of rainfall fail. The rain gauge records of the country have been made but for a brief period, and the stations have been widely scattered, so that no very definite conclusions can be drawn from them, but so far as they are of value they fail to show any increase. But if it be true that increase of the water supply is due to increase in precipitation, as many have supposed, the fact is not cheering to the agriculturist of the Arid Region. The permanent changes of nature are secular; any great sudden change is ephemeral, and usually such changes go in cycles, and the opposite or compensating conditions may reasonably be anticipated.