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powerplants, and their appurtenant works. The design and cost estimates for Hooker Dam and Reservoir on the Gila River and Charleston Dam and Reservoir on the San Pedro River were updated to July 1961 price levels. The present plan of development provides for the conveyance and delivery of Colorado River water through the main project canal system, extending from Lake Havasu to its terminus at Tucson, Arizona. This plan eliminates the previously contemplated arrangement for exchanging Colorado River water for Salt River water, in which the exchanged Salt River water would have been delivered through the Salt-Gila Aqueduct. This major change in project formulation resulted in part from the necessity for relocating about 80 miles of the Granite Reef Aqueduct to a higher elevation around the metropolitan area of Phoenix, Arizona, to avoid urban developments which have encroached upon the original canal location through this area. The geographically designated service units used in the original report have been abandoned in favor of hydrologic study areas which encompass the total land area affected by local water supplies and present uses, and are in need of an augmented water supply. These hydrologic study areas, having common surface-and ground-water supplies, have been adopted to demonstrate the need for Colorado River water which could be made available by direct diversions or exchange arrangements. The present plan contemplates the sale of Colorado River import water at a canalside delivery point on a cost-per-acre-foot basis. Arrangements would have to be made between upstream and downstream water users to effect the exchange of local supplies diverted at higher elevations for Colorado River water delivered to lower elevations through project canals. No attempt has been made in this report to delineate lands or areas to which specific quantities of water would be delivered. A complex and 7Epson Perfection 4870 Photo, 400 dpi, 8 bit, 14,174,208 byte