Africa has diverse geography, including mountains along the northern coast and eastern region, the Sahara Desert, savannas with unreliable rainfall, and rainforests with warm temperatures and heavy rainfall. The Great Rift Valley contains deep canyons surrounded by mountains. Several early African kingdoms emerged, including Ghana near the west coast which traded gold for salt with Muslims and engaged in ivory and slave trades with Berber nomads. Mali rose as a strong empire along the same region as Ghana, trading salt and gold; under Mansa Musa's rule from 1312 to 1337, Mali doubled in size and Timbuktu became a center of Muslim learning. Later, Songhai conquered Timbuktu and