Geographically, the Mississippi drains all or parts of 31 U. S. states stretching from the Rocky Mountains in the west to the Appalachian Mountains in the east and from the Canada-U.S. border on the north to the Gulf of Mexico on the south. It's the 4th longest river in the world and the 10th most powerful.Its largest tributary, the Missouri River, known as the River of the Big Canoe, flows in from the west. Here's a ballad about the history and significance of the Missouri.