 It spans of length as measured using its northernmost west fork, the Missouri River, which starts in the Rocky Mountains in Montana, joining the Mississippi proper in the state of Missouri.The Ohio River and Tennessee River are other tributaries on its east, and the Arkansas, Platte and Red River of Texas on the west.The Mississippi itself starts at Lake Itasca in Minnesota, and the river wends its way through the center of the country, forming parts of the boundaries of ten states, dividing east and west, and furthering trade and culture.