The Triassic basin of Mohammedia-Benslimane-ElGara-Berrechid contains a sedimentary series consisting of a sandy-conglomeratic formation (Formation A) at the base, surmounted by an argillaceous-saliferous formation (Formation B), the whole being capped by Late Triassic-Early Jurassic basalts. Formation (A) is formed by conglomeratic facies with alternations of sandstone in the middle and top of the formation. Formation (B) is subdivided into two members: (1) mudstone-siltstone member formed by alternations of mudstone and siltstone facies; and an argillaceous-saliferous member (2) composed by mudstone and evaporite facies. Sedimentary analysis carried out on more than ten outcrops and on four cores sample that have identified fifteen types of facies and seven architectural element and facies associations. It leads to the reconstruction of depositional environments during the Upper Triassic in the basin. Also, this work allowed a comparison of the sedimentary series of this basin with those of the other basins of the Moroccan Atlantic margin on one side and the North-east American margin on the other side.