The South Cameroon Plateau or Southern Cameroon Plateau is the dominant geographical feature of Cameroon. The plateau lies south of the Adamawa Plateau and southeast of the Cameroon Range. It slopes south and west until giving way to the Cameroon coastal plain in the southwest and the Congo River basin in the southeast. The plateau is characterised by hills and valleys in the southwest and a more gentle peneplain in the southwest. Isolated massifs occur, especially in the southwest. Metamorphic rocks make up the plain's basement. The soils are ferrallitic and lateritic, with colouration ranging from red or brown in the interior to yellow on the coast. The soils are subjected to silica leeching, so they are not productive without fertiliser.