From its source in the highlands of the , the Gambia follows a winding course to its mouth, which is a ria, or drowned estua.... river flat

The dividing and reuniting of river channelsa phenomenon known as braidinghas created several islands along the river's middle course, of which the two largest are Elephant Island and . The river valley is cut into a plateau of sandstone dating from the Tertiary period (66.4 million to 1.6 million years ago). Dense mangrove swamps fringe the lower river for 60 miles (97 km) inland, after which freshwater swamps and salt flats on low-lying stretches alternate with dense clumps of small trees and shrubs that line the cliffs. The river abounds in fish and river The grass-covered river flats (known locally as ) of the lower river are rendered useless for cultivation by the salt water that periodically inundates them, and settlements on them are few. The flats of the middle and upper river are of some agricultural value, however. Cultivation and settlement have therefore taken place in the middle flats and on the higher slopes, with many villages being located on the borderline b! etween the flats and the plateau, thus avoiding both the flooding of the lower slopes and the increasing aridity of the higher terrain. river flat