The rediscovery of America by the Genovese Christopher Columbus and the conquest of Mexico by the Spaniards was followed by a more gradual, but equally relentless, occupation of North America by the French and the British. The last phase of this process involved the discovery and exploration of the western Cordillera of North America. Fur traders Anthony Henday (1754) and the La Verendrye brothers (1743) were the first non Indians to sight the western Cordillera, while James Cook (1778) and Vitus Bering (1728,1741) were the first to explore the coasts of the northern Pacific beyond a California that was already discovered and subdued by the Spanish. There followed many expeditions that were driven by the search for gold and the fur trade as well as political and missionary interests. Most spectacular perhaps was the first crossing of the Canadian Cordillera by the Scot, Alexander MacKenzie, who reached the Pacific near Bella Coola, British Columbia in 1793. In his footsteps, the expeditions of Simon Fraser (1807), David Thompson (1807–1812), and others led to the geographic reconnaissance of the Cordillera of the northwestern United States and Canada. Lewis and Clark (1804–1805), who traversed the northwestern U.S. Cordillera, were the first who, while obviously involved in a politically motivated expedition, had an important charge to also make scientific observations. Thus, the western Cordillera had first to be “discovered” through the arduous efforts of many early explorers before any significant geological studies could be undertaken. The first geological map of North America, published by Jean Etienne Guettard in 1752 in his “Mémoire dans lequel on compare le Canada à la Suisse,”

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The present work aims (1) at documenting, by regional seismic transects, how the structural style varies in the western High Atlas system and its prolongation under the present-day Atlantic margin, (2) at understanding how this variation is related to the local geological framework, especially the presence of salt within the sedimentary cover, and (3) at discussing the exact geographic location of the northern front of the western High Atlas and how it links with the most western Atlas front in the offshore Cap Tafelney High Atlas. Previous work showed that the structural style of the Atlas belt changes eastward from a dominantly thickskinned one in central and eastern High Atlas and Middle Atlas of Morocco to a dominantly thin-skinned one in Algeria and Tunisia. We propose here to show that a similar structural style change can be observed in the other direction of the Atlas Belt within its western termination, where the western High Atlas intersects at right angle the Atlantic passive margin and develops into a distinct segment, namely the High Atlas of Cap Tafelney, where salt/evaporite-based décollement tectonics prevail. To cite this article: M.

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