Water received from underground resources, Solomonville Valley-Continued. REPORT ON HYDROGRAPHIC INVESTIGATION OF GILA RIVER BASIN IN COOPERATION WITH THE UNITED STATES INDIAN SERVICE, 1914-15. [By C. O. Jacob, district engineer.] This investigation is confined to that part of the Gila Basin above the eastern boundary of the Gila River Indian Reservation. This stream drains an area of varied topography and physiography, and general statements applying to the basin as a unit are impossible. It is really a complete river system made up of a number of minor basins whose individual characteristics have very little in common. The upper San Francisco and the Gila above the Red Rock Valley are typical mountain streams, although they, in common with all streams of the Southwest are subject to sudden and more or less violent floods resulting from heavy rainfall concentrated over small areas. They both maintain fairly steady flows throughout the spring months, subject to the sudden fluctuations in stage just mentioned. If we accept the theory of " forest storage" of rainfall the explanation of both these conditions follows readily, since both drainag areas are made up of heavily forested areas and also barren areas of igneous rock with steep slopes. The San Francisco and upper Gila occupy canyons eroded through Tertiary gravels, conglomerates, and lavas, and frequently through the older formations. These canyons vary considerably in width, and in a few places small valleys have been formed where the land is cultivated. The largest of these cultivated areas is the Duncan Valley, which lies both in Arizona and New Mexico. Below the junction of the two streams the river occupies a box canyon about 20 miles in length, changes direction to the northwest, and traverses the long, narrow central Gila Valley to its junction with San Carlos Cr ek. This latter stream drains an area of steep slopes and plateaus built up principally of recent lava flows, and generally barren. Its normal flow, therefore, is very small, and it also is subject to sudden. floods. The central Gila Valley is confined on the southwest by a mountain range drained by numerous short canyons and washes whose slopes decrease rapidly as they pass through the foothills to the valley. There are a few small streams more or less permanent in character in the upper reaches of some of the larger canyons, but this water is lost in the débris of the foothills and upper mesas. Below San Carlos the Gila River occupies another box canyon until it passes the buttes above Florence, where it enters the lower Gila Valley. This valley has been formed by a process of aggradation in which the original topography has become obliterated, and only the higher ridges and peaks of what were once mountain ranges are visible above the deposits of débris constituting the present valley fill. The San Pedro River, the most important tributary from the south, joins the main stream in the canyon about 25 miles below San Carlos. While its normal discharge at its mouth is very small, this stream is subject to unusually heavy floods, particularly in the winter, when the broad desert areas which it drains have become saturated by prolonged rainfall, so that a high percentage of the subsequent precipitation is carred off by the stream. The effect of this stream on the flow of the Gila River during the floods of December, January, and February, 1915, is particularly noticeable. In addition to the streams mentioned above, there are many other minor stream courses normally dry, which contribute to the flow of the main stream frequently throughout the year in a complex manner depending on the distribution and intensity of the local rainfall. We can expect, therefore, to find the flow of the Gila River erratic, particularly during times of considerable rainfall. Parts of the three principal Gila valleys, as well as several smaller areas, are being irrigated from the Gila River. The water is diverted directly from the stream by brush dams, each canal having its own heading. The distribution of the water to the various canals is handled independently in each valley, and in general it can be stated that the canals of each valley, considered as a unit, take all the water from the river they can get. The effect of this diversion on the stream flow during periods of high water is not apparent, due principally to the fact that in flow from washes and dry canyons and seepage and evaporation losses from flooded river bottoms can not be estimated. During periods of low water, however, the effect of the diversion becomes very apparent; painfully so to parties in the lower valleys. For example, we have for the dry months of May and June for the past four years the following mean daily discharges in second-feet: |