The GILA River is a tributary of the Colorado River located in the southwestern United States. It is the sixth-longest river in the United States and the largest tributary of the Colorado River, with a length of 649 miles. The GILA River originates in western New Mexico and flows through Arizona before emptying into the Colorado River near Yuma, Arizona. The GILA River watershed covers an area of over 60, 000 square miles and is home to a variety of wildlife, including bighorn sheep, bald eagles, and desert tortoises.