The San Francisco River is a river in the southwest United States, the largest tributary of the Upper Gila River. The Southwestern area of the United States could be defined as the states west of the Mississippi River, with the qualification of a certain northern limit such as the 37 The United States of America —commonly referred to as the The Gila /'hilə/ River ( O'odham [Pima]: Gila Akimel) is a Tributary of the Colorado River, 650 Miles (1044 Kilometers The river originates in New Mexico and enters the Gila down stream from Clifton, Arizona. New Mexico ( is a state located in the southwestern region of the United States of America. Clifton is a town in Greenlee County, Arizona, United States, on the San Francisco River.