The Missouri River, a major tributary of the Mississippi, flows east from the Rockies and eventually reaches the Atlantic via the Gulf of Mexico.

The Missouri River originates in the Rocky Mountains and flows generally eastward. It eventually joins the Mississippi River, which then flows south into the Gulf of Mexico. Since the Gulf of Mexico is part of the Atlantic Ocean, the Missouri River is considered to be part of the Atlantic drainage system, even though its source is on the east side of the Continental Divide. The other rivers listed flow west to the Pacific Ocean.