Drainage in the Colorado River Basin

The Green, Gila, and San Juan River Drainage Basins are the major tributaries to the Colorado River Basin drainage.  The maps above are out of propotrion with each other, particularly the San Juan, but give a general indication of their drainage areas when compared to the map of the entire basin on the right.

These maps show that the Grand River (present-day Colorado above its confluence with the Little Colorado) has a very small drainage basin compared with the other basin tributaries (the Green alone is 70% greater).  However, it should also be noted that spring snow-melt in the Rockies through the Yampa, Green, and Colorado Rivers is the major contributor to basin drainage.

Lesser tributaries, including the Virgin, Gunnison, and Little Colorado during White Mountains snow-melt, combine to make a significant contribution to the basin.