Red River of the South

The Red River, or sometimes the Red River of the South, is a major river in the Southern United States. It was named for its reddish water color from passing through red-bed country in its watershed. It is one of several rivers with that name. Although once a tributary of the Mississippi River, the Red River is now a tributary of the Atchafalaya River, a distributary of the Mississippi that flows separately into the Gulf of Mexico. This confluence is connected to the Mississippi River by the Old River Control Structure.

The south bank of the Red River formed part of the US–Mexico border from the Adams–Onís Treaty until the Texas Annexation and the Treaty of Guadalupe Hidalgo.

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