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Although various Indian tribes had been irrigating lands along rivers and streams in Arizona for many centuries, the first white settlers began diversions in the mid-1800's. Throughout the remainder of the century, canals were extended and new canals built that increased the irrigated acreage. In the 1890's, alternating severe flood and drought conditions beset the Salt River Valley. The tenacity and determination of the people resulted in the formation of an organization pledged to rebuilding its agricultural enterprise. Following enactment of the Reclamation Act of 1902, Arizona, still a territory, immediately moved forward. Construction of Theodore Roosevelt Dam in the Salt River Canyon was started in 1905 and was completed in 1911 by the Bureau of Reclamation. In 1917 the Salt River Valley Water Users' Association assumed responsibility from the Bureau of Reclamation for the operation and maintenance of the Salt River Project. The Association also undertook the responsibility of distributing the Project's water and power supply. Between 1922 and 1930 the Salt River Project constructed three additional dams in the Salt River Canyon with funds obtained by separate bond issues. These dams, with power-generating facilities included, increased the electrical supply to the valley for pumping from the vast underground water supply. Bartlett Dam on the Verde River was constructed in the period 1935 to 1939 by the Bureau of Reclamation, and Horseshoe Dam was constructed from 1944 to 1946. The flow of the Gila River was also inclined to flood and drought cycles and could not be depended upon to provide a firm water supply during summer irrigation periods. In 1929 the Bureau of Indian Affairs started construction of Coolidge Dam on the Gila River to store and regulate the riverflows for beneficial use of the Gila River Indian Reservation and non-Indian lands in the San Carlos Irrigation and Drainage District. The relative rights between upstream and downstream water users were settled in 1935 upon the entry of the Gila River Decree. In the Salt and Gila Valleys of central Arizona, ground-water development has continued since early days. The advent of the turbine pump and the production of inexpensive electrical energy made deep-well pumping feasible. Many thousands of additional acres of land have been developed in the past several decades which depend upon ground water alone. The net result has been a steady decline in the ground-water table throughout central Arizona, as the ground-water reservoirs are being depleted year by year. This accelerated decline in water levels has, in turn, resulted in land subsidence. II-4Epson Perfection 4870 Photo, 400 dpi, 8 bit, 14,174,208 byte