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The precepts under which the Department of the Interior has historically acted have never encouraged the development of one area to the detriment of another. The diminishing of an existing economy, or the retarded development of another, carries nationwide implications. In the Pacific Southwest, defined for the purposes of this study as portions of each of the above five States--each dependent to some extent on the Colorado River--it is incumbent upon the Secretary of the Interior in any plan of regional water development to preserve, protect, and promote the economy and interests of all the affected States. All water exportations from areas of surplus to areas of deficiency should protect the areas of origin within the States and the States themselves. This protection could be in the form of legislative policies recently adopted by the Congress in connection with the New Melones Project authorized by the Flood Control Act of 1962 (P.L. 87-874), in which diversions of water would be subordinate to all existing and anticipated future needs. The greatest future water requirements of the region will be for municipal and industrial uses, caused by the Nation's fastest rate of population growth. Other important needs are for irrigation, power, and flood control. The development plans presented in this report include water supplies for recreation, fish and wildlife, and cultural activities which we consider also essential to the well-being of an expanding population. There is not enough water available to the region at economic cost to provide for an expansion of irrigated acreage, except on Indian reservations and limited areas having local water supplies available. However, because of the importance of agriculture to the region, a major objective is to augment the water supplies to maintain irrigated agriculture as close as possible to present levels. Many crops are grown in the Pacific Southwest that cannot be grown elsewhere in the Nation or do not have proper market relations. The region presently has a total developed water supply of 16,410,000 acre-feet annually, This is 1,340,000 acre-feet less than the present demand of 17,750,000 acre-feet. Demand will increase to 20,120,000 acre-feet by 1975, 22,050,000 acre-feet by 1990, and 23,360,000 acre-feet by the year 2000--or 6,950,000 acre-feet more than the present supply. In the meantime, the flows of the Colorado River available to the lower basin will diminish steadily because of continuing development in the upper basin within its Compact entitlement. The California State Water Project will provide 1.9 million of the nearly 7 million acre-feet that must be added by the year 2000. The balance will have to come from improved water management and from new sources. 2Epson Perfection 4870 Photo, 400 dpi, 8 bit, 14,364,672 byte