Algeria covers an area of about 2.4 million km2, supporting a population of about 36 million people. They are concentrated along the northern seaboard, where the capital, Algiers, is located. The Atlas Mountains in the north of the country border the Mediterranean and comprise two main ranges which are separated by a high plateau. The highest peaks rise to 2,500 m. To the south, lies the Sahara Desert, which is cut by a northerly trending divide that separates it into two arid depressions covered in sand dunes: the eastern desert lies at an altitude of about 600 m, while the western one locally drops below sea level. The Hoggar Mountains in the far south rise to as much as 3,000 m, exposing geological sequences that give a clue as to what lies beneath the deserts.