The Tassili N’ Ajjer of southeastern Algeria consists of large areas of sand dunes and substantial areas of sandstone bedrock outcrops. This photograph vividly displays the differences between these two major landforms. The orange, complex, linear Tifernine Dunes with superimposed star dunes were named for the intermittently-flowing, south-to-north Tifernine watercourse along the southwestern extent of the dunes. This very distinctive alignment of sand dunes provides Space Shuttle astronauts a land reference in the much larger Sahara Desert. The dark, weathered sandstone rocks that border the Tifernine Dunes to the east and southwest have deep, narrow ravines that comprise a well-entrenched drainage pattern through the higher elevations of the plateau southwest of the dune field. This erosion process began millions of years ago when the climate was much wetter. This region now receives less than 1 inch (2.5 centimeters) of rainfall annually.