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OOiJlu~ III. Environmental Consequences A. Description of the Physical Environment The CRB encompasses a rich array of the most diverse aesthetic and pro- duct ive resources in the Un ited States. The seven Bas inStates are Wyoming, Utah, Colorado, Nevada, New Mexico, Arizona, and California. However, the productivity and carrying capacity of the Basin are tempered and controlled by its arid and semiarid climate. For all practical purposes, water resources development has dictated the future of the Basin since the turn of the century. A 1979 report by the Comptroller General describes the Basin succinctly. "The Colorado River originates in the Rocky Mountains of Colorado and Wyoming, flows southwest about 1,400 miles, and empties into the Gulf of California. It drains an area of 242,000 square miles in seven States, which represents one-twelfth of the area of the United States, excluding Alaska. The basin has climatic extremes of year-round snow cover and heavy precipitation on the high peaks of the Rockies and desert conditions with very low precipitation in southeast California and southwest Arizona. The Colorado River is controlled by several dams and reservoirs. The Glen Canyon Dam and lake Powell store most of the Upper Basin's water and control releases to the lower Basin. The Hoover Dam and lake Mead store most of the lower Basin's supply and control the amount of water released to lower Basin users." [7] Approximately 60 percent of the Upper Basin land area is under Federal administration, 15 percent is Indian Trust land, and 25 percent of the area is State, corporate, and individual land. The Bureau of land Management and the Forest Service administer about 58 percent of public land, most of it under the multiple-use doctrine. Grazing and crop production are two of the most important land uses. Forests cover about one-third of the area. Extensive outdoor recreation use is made of both public and private lands. Historically, the Basin has been sparsely populated. However, the population began to increase significantly about 1965. Since the 1980 census, the increases have been attributed to the so-called Sun Belt phenomena. However, the most dramatic local population growth patterns are related to expanding energy development industries. Service indus- tries accommodating the energy and recreation sectors also account for a significant portion of the population growth. B. Description of Precipitation and Climatic Conditions* "The annual river flow at lee's Ferry, Arizona, has fluctuated from a low of 5.6 to a high of 24.5 million acre-feet during * This section is taKen from an analysis by Gerard A. Klazura of the Division of Atmospheri c Resources Research, Bureau of Rec 1 amat i on. See "B i b 1 i ography from Klazura memorandum" for reference numbers. 7 ----- - - - - - - ----- - - - - - - - - - - -