Named for the reddish color of the water, the Red River flows through the southern United States, including the states of Texas, Oklahoma, Arkansas, and Louisiana. It serves as the border between Texas and Oklahoma east of of Texas's panhandle. The water's red color comes from passing through the red-bed country (sedimentary rocks that are red due to ferric oxides). In 1806, Thomas Jefferson commissioned the Red River Exploration to explore the lands newly acquired in the Louisiana Purchase.