evidence: Cameroon can be divided into northern, central, southern, and western geographic regions. North of the Benue (Bénoué) River, the savanna plain that occupies the country’s centre declines in elevation as it approaches the Lake Chad basin. The region contains scattered inselbergs, mounds of erosion-resistant rock that rise above the plains. The Gotel Mountains of the Adamawa Plateau trend from south to north, culminating in the Mandara Mountains of the northwest. [...] The western region extends north and west from the Sanaga River and continues north along the Nigerian border as far as the Benue River. The relief is mostly mountainous, the result of a volcanic rift that extends northward from the island of Bioko. Near the coast, the active volcanic Mount Cameroon rises to the highest elevation in western Africa—13,435 feet (4,095 metres). The rivers of Cameroon form four large drainage systems. In the south the Sanaga, Wouri, Nyong, and Ntem rivers drain into the Atlantic Ocean. The Benue River and its tributary, the Kébi, flow into the Niger River basin of Nigeria. The Logone and Chari rivers—which form part of the eastern border with Chad—drain into Lake Chad, whereas the Dja River joins the Sangha River and flows into the Congo River basin.