The constant wind of the central Sahara has clustered its moving sand in great oblate dunefields called Ergs. This …one is in the southwestern corner of Libya, and is spilling downwind into a rift valley. This area was a populous node during pluvial times which were associated with the continental glacial advances. Several important archeological sites are found in the Acacus area immediately beneath the lower left corner. The area is also underlain by extensive oil reserves.