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SETTING The PVID is in southeastern California, in Riverside and Imperial Counties, adjacent to the Colorado River. A privately developed irrigation project, the agricultural lands extend about 30 miles along the Colorado River with a 10-mile width at the widest point. Approximately 92,000 acres are irrigated. The climate of the area is typical of the deserts of the Southwest with hot dry summers and moderate to cool winters, The growing season is year-round. Average annual precipitation at Blythe in the north-central part of the district is approximately 4 inches per year, most of which occurs as thunder- showers during the summer. The principal cities within the irrigation district boundaries are Blythe, Ripley, and Palo Verde. U.S. Highway No. 60 (Interstate 10) runs east-west through Blythe and U.S. Highway No. 95 provides service north of Blythe. Physiography Irrigated lands in the District are mainly on the valley floor adjacent to the river. The topography of the valley floor may be characterized as flat, with a mild slope to the south of about 2 feet per mile. Its elevation ranges from 270 to 220 feet above sea level. It is bounded on the east by the Colorado River and on the west by a steep escarpment 80 to 120 feet high. There are some agricultural lands on Palo Verde Mesa west of the valley. The valley floor is the former flood plain of the Colorado River and is underlain by hundreds of feet of alluvium. Soils in the Palo Verde Valley range in texture from fine sand to silty clay and are excellent for crop production. Generally, the course-textured soils are utilized for the production of vegetables and melons, while the fine- textured soils are ideal for hay, cotton, wheat, and certain other grain crops. The coarse-textured soils occur adjacent to the Colorado River, and the fine-textured soils are located near the mesa on the western edge of the District. Prior to completion of Hoover Dam in 1935 and subsequent regulation of the Colorado River, lands within the Palo Verde Valley were frequently flooded during the spring months. This flooding created a high ground-water table and bogs and sloughs developed. As water was utilized by phyreatophytes, such as salt brush, arrowweed, and tules, salt concentrations in the soil and ground water increased. Salts were carried upward through capillary movement of water and deposited on the surface and in upper levels of the soil profile as the water evaporated. Irrigated agriculture is the primary economic sector in the District, and a variety of field crops and vegetables are grown. Alfalfa, cotton, and wheat are the major field crops. Major vegetable crops are lettuce, onions, and melons. Multiple cropping, including livestock grazing following harvests, occurs on approximately 32 percent of the irrigated land. 002929 3