West Africa is made up of plains and some low and high mountains. The region has four climate zones - the Sahara desert in the north, the dry Sahel grasslands, the savanna with grass, trees and tsetse flies, and the coastal rainforests. The Niger River is the most important river, flowing east and south for 2,600 miles through West Africa and watering the region via its inland delta of channels, swamps and lakes. West Africa has mineral resources like diamonds, gold, and oil, with Nigeria being a major oil exporter accounting for 95% of its exports.