Watersheds & River Basins

A watershed, or drainage basin, is all the land whose rain and snowmelt funnel into a single river system and out to the sea. The United States is carved into a handful of great basins, by far the largest of which is the Mississippi River watershed - an immense funnel covering more than 40 percent of the contiguous country, gathering water from 31 states between the Rockies and the Appalachians and pouring it into the Gulf of Mexico.

Other major basins drain to the Pacific (the Columbia and the Colorado), to the Atlantic seaboard, to the Great Lakes and the St. Lawrence, and northward to Hudson Bay. The ridgelines that separate them are the continental and lesser divides. The marker here sits at St. Louis, near where the Missouri and the Mississippi - the two longest rivers in the country - join to anchor the heart of that enormous central watershed.

• The Continental Divide
  The Great Divide of the Rocky Mountains related
• The Mississippi River
  The great river that drains the American heartland related
• The Mississippi Valley
  The great alluvial valley of the lower river related
• The Missouri River
  The longest river in North America related