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Abstract

A regional survey of emerged Pleistocene marine terraces, with emphasis on chronostratigraphic data, permits documentation of recent deformation in coastal areas adjacent to the plate boundary of northwestern Mexico.

During the last million years, the eastern coast of the Gulf of California, on the North American plate, remained vertically “stable,” whereas the Baja California peninsula was subjected to a slow and fairly continuous uplift. As a whole, the peninsular block has been uplifted at a mean rate of approximately 100 mm/103y in the past million years. However, uplift rates seem to have decreased, at least locally, based on the relative stability of the late Pleistocene terrace (ca. 125,000 years BP) in several areas of the northeastern, southern, and west central parts of the peninsula.

During the late Quaternary, the most deformed and uplifted areas were located close to the main fracture zones—in north westernmost Baja California (between the Agua Blanca and Rose Canyon-San Miguel fault systems), in the westernmost Vizcaino region (along the Bahia Tortugas fault, related to the Tosco-Abreojos fault system), and in the Colorado delta region (along the Cerro Prieto fault system). Strong uplift and warping motions also occurred in the Santa Rosalia area, but these are controlled by volcano-tectonic events related to the La Reforma Plio-Quaternary caldera.

The Baja California peninsula behaved as one large crustal block, in near-isostatic equilibrium, and was much less deformed than the California coast. This block has not been tilted westward since the Pliocene. This study supports the concepts that the peninsula is not completely attached to the Pacific plate, and that there is some plate motion along the western continental margin of Baja California.

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