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<br />4 <br /> <br /> <br />tQ <br />tQ <br />00 <br />CO <br /> <br />Development of the water resources in the Colorado River Basin took. <br /> <br />place gradually from the beginning of settlement around l860 and <br /> <br />has been continuing. In the Upper Basin, 1.4 million acres were <br /> <br />irrigated by 1920. The pace of development slowed thereafter with <br /> <br />the result that in 1965, l.6 million acres were under irrigation. <br /> <br />In addition, the water exported from the Upper Basin amounted to <br /> <br />about 500,000 acre-feet per year and consumptive use of water for <br /> <br />municipal and industrial purposes depleted about 30,000 acre-feet <br /> <br />per year. <br /> <br />Initial development in the Lower Basin was slow because of difficult <br /> <br />diversions from the Colorado River and its widely fluctuating flow. <br /> <br />Ilowever, with the completion of the Boulder Canyon Project in the <br /> <br />1930's, the development accelerated and abollt 1.3 million acres are <br /> <br />now under irrigation. In this regard, the Colorado River now pro- <br /> <br />vides 75 percent of the water to southern California where ~ore than <br /> <br />half of that State's 20 million people live. <br /> <br />The importance of salinity in water s~plies was recognized as early <br /> <br />as 1903. At that time, the initial work was done to identify desir- <br /> <br />able salinity levels for maintenance of crop production under irri- <br /> <br />gation. A limited amount of water sampling and analysis of the river <br /> <br />was being performed, primarily by t~~ Geological Survey. The main <br /> <br />purpose of these early tests was to evaluate the suitability of the <br /> <br />water supply for irrigation and other uses. In ti~e, it became clear <br />