Which two natural features form the boundaries of the Mississippi River drainage basin on the east and west?

If you want to get geographical you have to configure in the Red River of the North which flows north unlike the Mississippi and it cuts the drainage basin short up north in the Minnesota/North Dakota area. Here is a link to show you a picture: http://toxics.usgs.gov/hypoxia/images/mississippi_river_watershed.gif The Rocky Mountains are in the west. They act as a barrier. The appalcian mountains in the east probably do as well.