mountain range in south-central Gabon, which rises to more than 3,300 feet (1,000 m) between the Ngounié and the Ogooué (Ogooué River) rivers and forms the country's main watershed. The range contains Mount Milondo (3,346 feet 【1,020 m】), which is 53 miles (85 km) southwest of Koula-Moutou. Other high points in the range are Mount Iboundji (3,215 feet 【980 m】) and Mount Mimongo (2,822 feet 【860 m】). The granite massif is named for the explorer Paul du Chaillu, who noted the mountains during his journeys up the Ngounié River (1855–65).