Guinea owes its frontiers mainly to the accidents of the late 19th-century partition of Africa and has no geographic unity. The country can be divided into four regions: Lower Guinea (Guinée Maritime), the alluvial coastal plain; Middle Guinea, the plateau region of the Futa Jallon (Fouta Djalon), deeply cut in many places by narrow valleys; Upper Guinea (Haute Guinée), a gently undulating plain with an average elevation of about 300 m (1,000 ft), savanna country broken by occasional rocky outcrops; and the forested Guinea Highlands (Guinée Forestière), composed of granites, schists, and quartzites, including Mt. Nimba (1,752 m/5,747 ft), the highest peak in the country, at the juncture of Guinea, Liberia, and Côte d'Ivoire. The Niger River and its important tributary the Milo have their source in the Guinea Highlands; the Gambia River and Senegal River (whose upper course is called the Bafing in Guinea) rise in the Futa Jallon.