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~ C~ i'"' Co: , c non-Indian M&I uses. The Andrus Modified for M&I Alternative (Alternative 4), provi des that duri ng shortages, 25 percent of the Indi an i rri gati on amount would be reduced until exhausted prior to a pro-rata reduction of the remaining Indian irrigation and tribal homeland amounts with all non-Indian M&I uses (no 510,000 acre-foot cap). The Secretary's proposed Indian allocation is a combination of these two shortage distribution formulas. Like the Andrus allocation, the proposed shortage distribution maintains the 510,000 acre-foot cap on non-Indian M&I use, as well as the 10 percent reduction in Indian irrigation use for the 11 tribes or communities affected by water servi ce contracts executed in December 1980 (all except the Gil a River Indian Reservation). However, like Alternative 4 (Andrus Modified for M&I Use), the Gila River Indian Reservation's allocation would be reduced by 25 percent prior to the pro-rata reduction. Like Alternative 4, the Proposed Action will require effluent exchanges where feasible and consistent with contract provisions. However, in addit i on to the exchanges with the Salt Ri ver and Gi 1 a Ri ver Reservati ons described for Alternative 4, the analysis for the Proposed Action also assumes exchanges between the city of Tucson and the San Xavier Indian Reservation. III. AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES A. General Project Area 1 Geography and Climate The CAP service area is generlly described as consisting of Maricopa, Pinal, and Pima Counties, an area which includes metropolitan Phoenix and Tucson, as well as most of the irrigated agricultural land of Arizona. Fewer than 20 of the 134 entiti es recorrnnended for all ocati ons by the six alternatives are found outside this three-county area. f) The project area lies within the Gila River watershed in the Basin and Range physiographic province of the Southwest. The Basin and Range Provi nce is characteri zed by mounta in cha i ns and all uvi ated valleys. Elevations range from about 500 feet to over 10,000 feet. Most of the project service area lies between elevations of 900 feet and 2,400 feet. The climate of this area is characterized by long, hot summers and short, mild winters; low annual rainfall; low relative humidity; high evaporation; and a high percentage of days with sunshine. The annual preci pi tati on averages about 8 inches. Temperatures vary, but summer temperatures above 100 degrees are common, and winter temperatures usually do not exceed 65 to 70 degrees. Q~'l 4