This mountainous region is located about south of the capital, Algiers. The area is largely rocky desert with an average elevation of more than above sea level. The highest peak, Mount Tahat, is at . The mountains are primarily composed of metamorphic rock approximately 2 billion years old, although there are areas where more recent volcanic activity has laid down much newer rock. Several of the more dramatic peaks, such as Ilamen, are the result of erosion wearing away extinct volcano domes, leaving behind the more resistant material that plugged the volcanic cores.