Which river is a major river of the southern Great Plains and forms most of the border between Oklahoma and Texas?

The Red River is a significant waterway that serves as a natural boundary for a substantial portion of the border between Oklahoma and Texas. Stretching approximately 1,290 miles, it originates in the Rocky Mountains of New Mexico and flows eastward, eventually emptying into the Mississippi River. The river's importance as a geographical and historical feature is highlighted by its role in delineating state lines and its significance in regional agriculture and water resources in the Great Plains.

In contrast, the Missouri River primarily flows through the northern United States, with its route far removed from the southern Great Plains. Similarly, the Mississippi River is a major river in the central U.S. but does not directly define the border between Oklahoma and Texas. The Snake River, located primarily in the western United States, is completely unrelated to this geographical context. This focus on the Red River reflects its significant role within the southern Great Plains region.