The topography of the Sahel is mainly flat; most of the region lies between 200 and 400 meters (660 and 1,310 ft) in elevation. Several isolated plateaus and mountain ranges rise from the Sahel, but are designated as separate ecoregions because their flora and fauna are distinct from the surrounding lowlands. Annual rainfall varies from around 100–200 mm (4–8 in) in the north of the Sahel to around 700–1,000 mm (28–39 in) in the south.[1]