This report gives the results of sediment-sampling studies of the Geological Survey in the Colorado River basin for the period from October 1, 1925, to September 30, 1941. Records are given for the entire period for the Grand Canyon gaging station and for shorter periods at other stations in the basin. The results reported consist of the records of the mean daily concentrations.of sediment for all stations, and in addition, the mean daily discharge and daily load of sediment for many of the stations.
The available records indicate that the runoff of the Colorado near Cisco, Utah, plus the runoff of the Green at Green River, Utah, plus the runoff of the San Juan near Bluff, Utah, amount to about 90 percent of the runoff at the Grand Canyon gaging station, but the sediment loads at the three upper stations amount to only about 60 percent of the sediment load at Grand Canyon. The Little Colorado River and two or three other unsampled tributaries probably are the major sources of the unmeasured sediment
Information is given concerning the sizes of the particles of the sediment at the Grand Canyon, Willow Beach, and Bluff stations during periods of this investigation.
The annual load at Grand Canyon during the 16 years ranged from 50,080,000 tons in 1933-34 to 480,000,000 tons in 1928-29, and the mean annual load at that station for the 16-year period was 200,200,000 tons. The mean annual runoff for the Grand Canyon station during the period was 12,640,000 acre-feet
