The Colorado River begins in the Rocky Mountains, collecting snowmelt as it meanders through an alpine valley. Across a vast swath of Colorado, Wyoming and Utah, the river grows as it takes in major tributaries: the Gunnison, the Dolores, the Green and others. The Colorado River Basin encompasses more than 246,000 square miles in seven U.S. states and northern Mexico. … Water diverted from the river flows from taps in Denver, Phoenix and Las Vegas and throughout much of Southern California, supplying nearly 40 million people. About 70% of the water diverted from the river in the U.S. is used for agriculture … The region’s heavy use of the river is colliding like never before with the climate, which is growing hotter and drier.