An extensive 'wilderness' area of desert sand-dunes, gravel outwash plains and mudflats, c.160 km long by up to 25 km wide (widest between Jabal Fidan and Umm Muthla). There is some open bushland of Acacia tortilis, A. raddiana and Ziziphus; Tamarix and Phragmites occur locally in the lowest areas. Main land-use is nomadic pastoralism, with a minor but increasing amount of irrigated cultivation. Large areas are military zones.