Located within the Mississippi Flyway, one of the nation's most important flyway routes, Mark Twain NWR provides waterfowl and other migratory birds with food, water and protection during the spring and fall migrations.The Refuge is separated into three Districts and a headquarters in Quincy, Illinois.The Annada District consists of the Clarence Cannon NWR and the Delair, Gardner, Harlow Island and Gregory Landing Divisions of Mark Twain. The District contains some of the last remaining large contiguous stands of bottomland hardwoods in the area. The Brussels District includes the Calhoun, Batchtown, Gilbert Lake, Portage Island and Apple Creek Divisions. The division includes a major archeological site, including two mounds. The Wapelo District includes the Big Timber, Louisa, Keithsburg and Horseshoe Bend divisions. Three Divisions, Big Timber, Louisa and Keithsburg, are located in the floodplains of the Mississippi River, while Horseshoe Bend is in the Iowa River floodplain.