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How did the Atlas Mountains form geologically?

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Map showing the Atlas Mountains across Morocco, Algeria, and Tunisia in North Africa, with color shading to indicate elevation changes. Major mountain ranges, cities, rivers, and physical features such as the High Atlas, Anti-Atlas, Saharan Atlas, and surrounding deserts are labeled. An inset locator map highlights the region's position in northern Africa. — Atlas Mountains The Atlas Mountains.

The Atlas Mountains are geologically complex, consisting of two distinct structural regions formed through different processes.1

The Tell Atlas

The Tell Atlas is a young, folded mountain range that continues to form today, as evidenced by ongoing seismic activity. It originated from a sediment-filled basin during the Paleogene and Neogene periods (approximately 65 to 2.6 million years ago). During this mountain-building process, layers of flysch—thick deposits of sandstone and clay—were pushed southward over a marginal rim.12

The Saharan Atlas

The Saharan Atlas belongs to the structural grouping of the African continent's ancient base rock. Its formation resulted from two primary processes:1
* Folding: The crust was crumpled into folds during the Jurassic Period and the Cretaceous Period.1
* Uplift: Mighty folding of the substructure raised fragments of the base rock, creating features such as the horst that constitutes the High Atlas of Morocco.1

These ranges are separated from the African Shield by a structural line extending from Agadir to the Gulf of Gabes.2