The northeastern extension of the Tassili N’ Ajjer is an austere, beautiful desert. From the dark, heavily eroded sandstone plateau in the southwestern quadrant of the photograph to the numerous drainage valleys filled with scattered sand sheets and sand dunes, the vivid desert colors range from dull red to black. The wide variety of colors results from desert varnish, which is a thin layer of metallic oxides dissolved from the rocks and deposited on the surface as a stain. This area in southeast Algeria is strategic because it is on the Algeria-Libya border. The border is visible near the center of the photograph in the gray area where very narrow lines could be a roadway, a fence line, or a combination of the two.