Assuming that you're referring to the villages in the Sahel during the era of Sahelian Kingdoms, a lot of them settled on the edge of Sahara, on its southern border to be precise. The southern border of Sahara is filled with forests and have enough resource to sustain their living. But they cant go any further because they were hindred by the Ashanthis and Yoruba
The western and eastern sierra nevada have substantially different species of plants and animals, because the east lies in the rain shadow of the crest. the plants and animals in the east are thus adapted to much drier conditions.
