Drainage in the Colorado River Basin

The Green, San Juan, and Gila River Basins are the major contributors to the Colorado River Basin drainage.  The Little Colorado (which has little flow other than during spring snow-melt in the White Mountains) fills in the drainage in Arizona.  Gunnison River Basin completes the drainage in Colorado (State), and the unnamed river north of Lake Mead is the Muddy.

It is interesting to note that Green River drainage is 70% greater than the Grand's (now the Colorado), and that the Grand Canyon was named after the river that ran through it before it was renamed, not because of its majesty and grandeur (see Satire on menu selection Navajo Bridge - History if you are interested in that story of intrigue).