In the southwest United States and extreme northern Mexico, the Rio Grande river is one of the two principal riverways. The other river is the
Colorado River.
Depending on how it is measured, the Rio Grande is either the fourth or fifth longest river system in North America, exceeded in length by the (1) Missouri-Mississippi river, (2) Mckenzie-Peace river and the (3) Yukon river. The (4) Saint Lawrence river is also about 1900 miles long.
The Rio Grande is also the 20th longest in the world.
Much like most of the border between Texas and Mexico, the Rio Grande river has change course countless times and flows a path entirely apart from the international boundary, some times as much as a mile from that boundary. The river has done the same thing in short distance where the west boundary of Texas begins.