mountainous plateau extending from the southern Fouta Djallon highlands through southeastern Guinea, northern Sierra Leone and Liberia, and northwestern Côte d'Ivoire (Ivory Coast). The source of the Niger (Niger River), the longest and most important river of western Africa, the highlands form the divide between the streams that flow northward to the Niger and those that flow southward to the Atlantic coast. The Niger itself rises in Guinea near the Sierra Leone border at an elevation of 2,500 feet (750 m) and less than 200 miles (320 km) from the Atlantic; several of its major tributaries (including the Milo, the Sankarani, and the Bagoé rivers) also originate in the Guinea Highlands.

Composed of granitic gneisses and quartzite, the well-watered plateau averages more than 1,500 feet in elevation and is covered with variegated rain forest and humid savanna. Several mountain ranges rise above its surface, including the Nimba Range (Mount Nimba, 5,748 feet 【1,752 m】) and Sierra Leone's Loma Mountains (Mount Loma Mansa, 6,391 feet 【1,948 m】) and Tingi Mountains (Sankanbiriwa, 6,079 feet 【1,853 m】), where its highest peaks are to be found.

The plateau is inhabited by people who cultivate rice, fonio (a crabgrass cereal), corn (maize), oil palm, coffee, and kola nuts. Large iron-ore deposits in the Nimba Range have been worked since the early 1960s.