The Atlas Mts. are a climatic barrier between the Mediterranean basin and the Sahara Desert. The slopes facing north are generally well watered and have important farmland and forests; on these slopes are the headwaters of many streams used for irrigation. The slopes facing south and the drier areas of the system are generally covered with shrub and grasses and have salt lakes and salt flats; sheep grazing is important there. The Atlas Mts. are rich in minerals, especially phosphates, coal, iron, and oil.
The Atlas Mountains (Kabyle: Idurar n leṭles, جبال الأطلس ) is a mountain range across a northern stretch of Africa extending about 2,400 km (1,500 miles) through Morocco, Algeria, and Tunisia. The highest peak is Jbel Toubkal, with an elevation of in southwestern Morocco. The second highest mountain is the M'Goun of . The Atlas ranges separate the Mediterranean and Atlantic coastlines from the Sahara Desert. The population of the Atlas Mountains are mainly Berber tribes in Morocco and kabyles in Algeria. The terms for 'mountain' in some Berber languages are adrar and adras, believed to be cognate with the toponym.
The mountains are divided into additional and separate ranges, including the Middle Atlas, High Atlas, and Anti-Atlas. The lower Tell Atlas running near the coast and the larger Saharan Atlas running further south terminate in the Aurès Mountains located in Algeria and Tunisia. The Atlas Mountains constitute one of the distinct physiographic provinces of the larger African Alpine System division.
The basement rock of most of Africa was formed in the Precambrian (approximately 4.5 billion to approximately 550 million years ago) and is much older than the Atlas mountains lying in Africa. The Atlas formed during three subsequent phases of Earth's history.
The first tectonic deformation phase involves only the Anti-Atlas, which was formed in the Paleozoic Era (~300 million years ago) as the result of continental collisions. North America, Europe and Africa were connected millions of years ago. The Anti-Atlas mountains are believed to have originally been formed as part of Alleghenian orogeny. These mountains were formed when Africa and America collided, and were once a chain rivaling today's Himalayas. Today, the remains of this chain can be seen in the Fall line in the eastern United States. Some remnants can also be found in the later formed Appalachians in North America.
A second phase took place during the Mesozoic Era (before ~65 My) and consisted of a widespread extension of the Earth's crust that rifted and separated the continents mentioned above. This extension was responsible for the formation of many thick intracontinental sedimentary basins including the present Atlas. Most of the rocks forming the surface of the present High Atlas were deposited under the ocean at that time.
Finally, in the Tertiary Era (~65 million to ~1.8 million years ago), the mountain chains that today comprise the Atlas were uplifted as the land masses of Europe and Africa collided at the southern end of the Iberian peninsula. Such convergent tectonic boundaries occur where two plates slide towards each other forming a subduction zone (if one plate moves underneath the other) and/or a continental collision (when the two plates contain continental crust). In the case of the Africa-Europe collision, it is clear that tectonic convergence is partially responsible for the formation of the High Atlas, as well as for the closure of the Strait of Gibraltar and the formation of the Alps and the Pyrenees. However, there is a lack of evidence for the nature of the subduction in the Atlas region, or for the thickening of the Earth's crust generally associated with continental collisions. In fact, one of the most striking features of the Atlas to geologists is the relative small amount of crustal thickening and tectonic shortening despite the important altitude of the mountain range. Recent studies suggest that deep processes rooted in the Earth's mantle may have contributed to the uplift of the High and Middle Atlas.
The range can be divided into three general regions from west to east:
The Middle Atlas is a portion of the Atlas mountain range lying completely in Morocco. The Middle Atlas is the westernmost of three Atlas Mountains chains that define a large plateaued basin extending eastward into Algeria. South of the Middle Atlas and separated by the Moulouya and Oum Er-Rbia rivers, the High Atlas stretches for with a succession of peaks among which ten reach above . North of the Middle Atlas and separated by the Sebou River, the Rif mountains are an extension of the Baetic Cordillera (Baetic mountains, which include the Sierra Nevada) in the south of Spain.
The High Atlas in central Morocco rises in the west at the Atlantic coast and stretches in an eastern direction to the Moroccan-Algerian border. At the Atlantic and to the southwest the range drops abruptly and makes an impressive transition to the coast and the Anti-Atlas range. To the north, in the direction of Marrakech, the range descends less abruptly.
On the heights of Ouarzazate the massif is cut through by the Draa valley which opens southward. In this chaos of rocks the contrasts are astonishing: water runs in some places, forming clear basins. It is mainly inhabited by Berber people, who live in small villages and cultivate the high plains of Ourika Valley.
The Anti-Atlas extends from the Atlantic Ocean in the southwest of Morocco toward the northeast to the heights of Ouarzazate and further east to the city of Tafilalt (altogether a distance of approximately ). In the south it borders the Sahara. The easternmost point of the anti-Atlas is the Djebel Sarhro mountains and its eastern boundary is set by sections of the High Atlas range.
The Saharan Atlas of Algeria is the eastern portion of the Atlas mountain range. Not as high as the Grand Atlas they are far more imposing than the Tell Atlas range that runs to the north of them and closer to the coast. The tallest peak in the range is the high Djebel Aissa. They mark the northern edge of the Sahara Desert. The mountains see some rainfall and are better suited to agriculture than the plateau region to the north. Today most of the population of the region are Berbers.
The Tell Atlas is a mountain chain over in length, belonging to the Atlas mountain ranges and stretching from Morocco, through Algeria to Tunisia. It parallels the Mediterranean coast. Together with the Saharan Atlas to the south it forms the northernmost of two more or less parallel ranges which gradually approach one another towards the east, merging in Eastern Algeria. At the western ends at the Middle Atlas range in Morocco. The area immediately to the south of this range is high plateau, with lakes in the wet season and salt flats in the dry.
The Aurès Mountains of Algeria and Tunisia are the furthest eastern portion of the Atlas mountain range.