*5.3. Extra-regional Tsunami Activity*

Deposits correlated with extreme wave action in other parts of the Mexico's Pacific coastline have raised the question as to whether a source from tsunamis can be distinguished from major storms [19]. In particular, the adjoining Jalisco and Michoacán states of Mexico far south of Baja California Sur are bordered by an active subduction zone resulting from compression between the Rivera lithospheric plate and the continental mainland. Among the historical events recorded for this region, the 22 June 1932 earthquake (magnitude 7.7) was one of the region's most destructive a ffecting an area 1 km inland along a 20-km stretch of coast with a run-up of 15 m [20]. In contrast, the Gulf of California has no historical record of tsunami events, although shallow earthquakes are relatively common due to transtensional tectonics associated with activity along multiple strike-slip faults that dissect narrow sea-floor spreading zones [5]. Traces of former subduction zones related to the San Benito and Tosco-Abreojos faults extend o ffshore along much of the outer Pacific coast of Baja California but these ceased to be active approximately 12 million years ago [5]. Rocky shores along the inner gulf coast of the Baja California peninsula close to the study site entail steep cli ffs that rise abruptly to elevations as high as 100 m (Figure 1c). Nothing has been described as remotely similar to the Pleistocene tsunami deposits documented with a run-up of 270 m against the steep volcanic shores of Santiago in the Cape Verde Islands [21]. The hypothesis of a tsunami origin for the Ensenada Almeja CBB is easily eliminated on account of the barren zone lacking boulders inside the partial-ring construction (Figure 5), as well as the occurrence of the CBB restricted to one side of Ensenada Almeja. Any potential tsunami source would have filled the interior of the half-ring with boulders. Moreover, comparable deposits can be expected to have formed along both sides of the bay.
