Suspended matter in the Colorado River, 1925–1935

The rugged topography of a great part of the Colorado River Basin is a significant factor in determining the quantity of water and suspended matter carried by the River. The mountainous regions of Colorado and Wyoming contribute a large part of the flow of the River, whereas the central part of the Basin, cut by deep gorges and canyons, contributes a large part of the suspended matter carried by the River.

The discharge of the Colorado River as measured near Cisco, Utah, with a drainage‐area of 24,100 square miles is slightly greater than the discharge of the largest tributary, the Green River, measured near Greenriver, Utah, with a drainage‐area of 40,600 square miles. The Green, however, carries a considerably larger load of suspended matter. Two other tributaries, the San Juan and Little Colorado rivers, each with a drainage‐area of about 25,000 square miles, carry large loads of suspended matter in proportion to their discharge. For example, the Little Colorado River in the summer of 1931 contributed less than 10 per cent of the flow of the main river at Grand Canyon, but the Little Colorado carried about 10,000,000 tons of suspended matter during this period and the main river had about 25,000,000 tons for the same period.