The fertile Tell is the country's heartland, containing most of its cities and population. Made up of hills and plains of the narrow coastal region, the several Tell Atlas mountain ranges, and the intermediate valleys and basins, the Tell extends eastward from the Moroccan border to the mountains of the Grande Kabylie and the Bejaïa Plain on the east. Its eastern terminus is the Soummam River. The High Plateaus and the Saharan Atlas
Stretching more than 600 kilometers eastward from the Moroccan border, the High Plateaus (often referred to by their French name Hauts Plateaux) consist of undulating, steppe-like plains lying between the Tell and Saharan Atlas ranges. The plateaus average between 1,100 and 1,300 meters in elevation in the west, dropping to 400 meters in the east. So dry that they are sometimes thought of as part of the Sahara, the plateaus are covered by alluvial debris formed when the mountains eroded. An occasional ridge projects through the alluvial cover to interrupt the monotony of the landscape.
Higher and more continuous than the Tell Atlas, the Sahara Atlas range is formed of three massifs: the Ksour near the Moroccan border, the Amour, and the Oulad Nail south of Algiers. The mountains, which receive more rainfall than those of the High Plateaus, include some good grazing land. Watercourses on the southern slopes of these massifs disappear into the desert but supply the wells of numerous oases along the northern edge of the desert, of which Biskra, Laghouat, and Béchar are the most prominent.
Eastern Algeria consists of a massif area extensively dissected into mountains, plains, and basins. It differs from the western portion of the country in that its prominent topographic features do not parallel the coast. In its southern sector, the steep cliffs and long ridges of the Aurès Mountains create an almost impenetrable refuge that has played an important part in the history of the Maghrib since Roman times. Near the northern coast, the Petite Kabylie Mountains are separated from the Grande Kabylie range at the eastward limits of the Tell by the Soummam River. The coast is predominantly mountainous in the far eastern part of the country, but limited plains provide hinterlands for the port cities of Bejaïa, Skikda, and Annaba. In the interior of the region, extensive high plains mark the region around Sétif and Constantine; these plains were developed during the French colonial period as the principal centers of grain cultivation. Near Constantine, salt marshes offer seasonal grazing grounds to seminomadic sheep herders.
The Algerian portion of the Sahara extends south of the Saharan Atlas for 1,500 kilometers to the Niger and Mali frontiers. The desert is an otherworldly place, scarcely considered an integral part of the country. Far from being covered wholly by sweeps of sand, however, it is a region of great diversity. Immense areas of sand dunes called areg (sing., erg) occupy about one-quarter of the territory. The largest such region is the Grand Erg Oriental (Great Eastern Erg), where enormous dunes two to five meters high are spaced about forty meters apart. Much of the remainder of the desert is covered by rocky platforms called humud (sing., hamada), and almost the entire southeastern quarter is taken up by the high, complex mass of the Ahaggar and Tassili-n- Ajjer highlands, some parts of which reach more than 2,000 meters. Surrounding the Ahaggar are sandstone plateaus, cut into deep gorges by ancient rivers, and to the west a desert of pebbles stretches to the Mali frontier.
Climate Northern Algeria is in the temperate zone and enjoys a mild, Mediterranean climate. It lies within approximately the same latitudes as southern California and has somewhat similar climatic conditions. Its broken topography, however, provides sharp local contrasts in both prevailing temperatures and incidence of rainfall. Year-to-year variations in climatic conditions are also common.
Climate: In the Tell, temperatures in summer average between 21° C and 24° C and in winter drop to 10° C to 12° C. Winters are not cold, but the humidity is high and houses are seldom adequately heated. In eastern Algeria, the average temperatures are somewhat lower, and on the steppes of the High Plateaus winter temperatures hover only a few degrees above freezing. A prominent feature of the climate in this region is the sirocco, a dusty, choking south wind blowing off the desert, sometimes at gale force. This wind also occasionally reaches into the coastal Tell.
In Algeria only a relatively small corner of the Sahara lies across the Tropic of Cancer in the torrid zone, but even in winter, midday desert temperatures can be very hot. After sunset, however, the clear, dry air permits rapid loss of heat, and the nights are cool to chilly. Enormous daily ranges in temperature are recorded.