Collection by the Geological Survey of records of stream flow in the Colorado River Basin was begun in August 1889, when three gaging stations were established in Arizona, on' the Gila, Salt, and Verde Rivers. In 1894-95 the work was extended to include 15 gaging stations, on tributary streams at points in the basin where irrigation development was most intensive, and by 1910 the number had increased to 109. In 1938 there were 262 gaging stations, located to advantage throughout the basin.
The earliest known records of discharge in the Colorado River Basin were individual measurements of the main river, made by engineers of the United States Army, 1 at Stone's Ferry near Boulder Canyon August 12, 1875, at Camp Mohave September 2, 1875, and at Fort Yuma March 20, 1876. In the summer of 1876, the Southern Pacific Co. established a gage near the railroad bridge over Colorado River at Yuma, and daily gage readings at that point, now available, are continuous since January 1, 1878.
Modern irrigation, using surface waters diverted from various streams in the basin, was begun many years before the first continuous records of discharge Had been obtained. As developments for irrigation and other purposes increased in size and number, became more systematized, and required greater knowledge of water supply, the collection of records of stream flow was substantially augmented through the assistance of many interested parties and agencies, both private and public.
