The Colorado River provides a valuable water resource to all or parts of seven western states. Degradation in the quality of Colorado River waters (particularly salinity) will have significant impact on the economics of these western states as well as on the political relations with Mexico which receives flow from the United States. In the late 19th century and early 20th century, sediment and salt loads in the Colorado River were high, however, during the 1940s there was a dramatic decrease in sediment discharge through the Grand Canyon and a decrease in salinity at Imperial Dam. It is hypothesized that the decrease in sediment load was caused by the progressive reduction in erosion on rangelands within the basin due to reduction of grazing and increased soil conservation techniques during the 1920s and 1930s. Experimental studies have shown that a reduction in sediment production from the headwater slopes of a basin is not reflected at the watershed outlet until stored sediment has been flushed from the channel network. In a similar manner it could be that the reduction of sediment production in the Colorado River Basin was not seen as a decrease in sediment discharge in the Colorado, Green, or San Juan Rivers until stored alluvium had been removed from tributary valleys. Geomorphic changes in tributary channels in the Colorado River Basin will indicate whether channel incision and sediment storage has occurred. Sites of natural sediment storage will also be sites of salt storage. Protection of these sites from future remobilization through channel incision and arroyo formation may prevent a repeat occurrence of the dramatic increase in sediment and salt loads seen in the 1950s and 1960s.The potential commercial application as described by the awardee: Results of the study will be of great significance to federal and state agencies involved in the management of land and resources in the Colorado River Basin. Results will also be of general financial value to the vast region drained by the Colorado River.