The Red River forms the entire southern border, other than the Panhandle area, between Oklahoma and Texas. Known as the "Rio Rojo" to the Spaniards, the river gets its color (and bitter taste) by cutting through gypsum, copper, granite, and red clay formations in the Lake Texoma area.
In the early 1700's, French explorers and traders were involved with Native Americans on the river and, in 1831, the steamboat "Enterprise" began to ferry cotton, grain, and passengers between Fort Towson, Fort Washita, and the Gulf of Mexico.
The Adam-Onis Treaty of 1819 set the Red River as the southern border of the Louisiana Purchase. Then, in 1923, the Supreme Court established the south bank as the border between Oklahoma and Texas.