The Rio Grande is one of the principal rivers in the southwestern United States and northern Mexico. Known in Mexico as the Río Bravo del Norte, it flows 3,051 kilometers from the San Juan Mountains of Colorado to the Gulf of Mexico. For much of its length, it serves as the natural international border between the U.S. state of Texas and the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas. The river is vital for irrigation in the arid regions it traverses, though its flow has been significantly reduced by heavy water use and a series of dams. Interestingly, because the river's channel can shift over time due to erosion and flooding, the U.S. and Mexico have had to sign several treaties to determine how the international boundary moves with the water, most notably the Chamizal Treaty of 1963.