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3 002277 Toward the end of ma.x:l.mum. productivity of water, information at hand BUffices for planning some early measures. Far lIIOre exacting, however, vill be the requirements for data and information on which to base continuing project operation and over-all ma.nagement of the water resource under conditions of full development, including sound adm1nistrative decision and COlII.Promise among 1IIIltually exclusive uses ot water. For such decision and cOlII.Promise the region is ill prepared. . The Geological Survey has done, and is doing, much toward acquiring such knowledge. Scope of this past and present accolII.Plish- ment vill be lIUIIDII8.l'ized. Jlecessary in regard to the lower Colorado region, however, is much more intensive and particularized investiga- tion, much of it pioneer inchara.cter. This particularized effort vill be outlined in a folloving list of progrlllll objectives. HYDROLOGIC IlWESTIGATIONS Past and Current Programs Records of streamflow in the lower Colorado River basin and service areas began with the measurement of the Colorado River at Yuma in 1902. 1I0w, records are maintained on all principal streams and many of the mitlor streams, mainly in cooperation vi th the States of Ari~ona lind California. In Arizona alone some 150 stations were active during 1963. These records, spanning some 4,500 station-years, form the hydrologic basis for development and operation of river-management projects. Analyses of river-water quality are 1Jl8.de at regular intervals at about ~ stations in the region. Thousands of analyses have been made during the past 20 yes:rs to define the chemical quality of ground waters. As wells are drilled in areas under study, additional samples are analyzed. In critical s:reas wells are re-sampled at intervals to . define quality changes. Ground water has been studied in numerous areas, especially those where substen;l;ial ground-water development has taken place. (See fig. 1). In Arizona, studies have been made in the Gila River and Salt River valleys near Phoenix, the Navajo and Papago Indian reservations, and the lower Santa Cruz River and Safford Valley s:reas. In southern California, studies are in progress in the Imperial Valley and in the Joshna Tree .ational Monument.