The Cahaba River is the longest substantially free-flowing river in Alabama and is among the most scenic and biologically diverse rivers in the United States. It is a major tributary of the Alabama River and part of the larger Mobile River basin. With headwaters near Birmingham, the Cahaba flows southwest, then at Heiberger turns southeast and joins the Alabama River at the ghost town and former Alabama capital of Cahaba in Dallas County. Entirely within central Alabama, the Cahaba River is long and drains an area of . The name Cahaba is derived from the Choctaw words oka meaning "water" and aba meaning "above" Geography The Cahaba River flows across three physiographic provinces of the state: Appalachian Plateau, Ridge and Valley, and Coastal Plain. The Mobile River basin has the largest Gulf Coast drainage basin east of the Mississippi River, and the Cahaba is one of the seven river systems that contribute to its flow. The mean discharge of water from 1938 to 2000 is about 80 m3/s. The average rainfall is 138 cm/yr. The terrestrial biome of the river is classified as eastern deciduous forest. Course The Cahaba River begins in the Valley and Ridge region bounded by the Piedmont to the southeast and the Cumberland Plateau to the northwest. It has two major physical regions: Upper and Lower Cahaba. The river empties into the Alabama River. The upper Cahaba forms roughly the first 100 miles, starting at the headwaters and continuing to the Fall Line, a region in which the Appalachian Mountains end and the Gulf Coastal Plain begins. It passes through Trussville, Leeds, Irondale, Birmingham, Mountain Brook, Hoover, Vestavia, Helena, West Blocton, and Centreville. The lower Cahaba begins at the fall line and continues through Selma and empties into the Alabama River at the former town of Cahaba.<ref name=Rivers>{{cite book |last=Jackson |first=Harvey H. III |title=Rivers of History-Life on the Coosa, Tallapoosa, Cahaba and Alabama |year=1995 |publisher=The University of Alabama Press |location=Tuscaloosa, Alabama |pages=50–52 |isbn=0-8173-0771-0 }}</ref> History Precolonization Located adjacent to the Cahaba River basin, the Moundville Archaeological Site (1000–1450 AD) was the second-largest community of the Mississippian culture. The Black Warrior River and the Cahaba River run parallel to each other for over 100 miles, often as close as 30 miles apart. The Bottle Creek Site (1250–1550 AD), located little more than 100 miles downriver in the Mobile-Tensaw River Delta, also influenced the region. A large mound