Abstract

The submarine geology of the continental margin at the tip of the peninsula of Baja California, Mexico, has been mapped through the use of continuous reflection profiling. A sequence of folded and faulted sediments, correlated with the Pliocene Salada Formation, unconformably overlies the volcanics and pyroclastics of the Comondú Formation and the granitic rocks of the Baja California pluton. Thirty-five dredge hauls, collected by Shepard from submarine canyons in the region, have substantiated these correlations. The structure of the continental terrace is dominated by normal faulting, trending northeast-southwest, which suggests uplift of the southern part of the peninsula. Cabrillo Seamount, lying to the southeast, is a detached granitic fault block. The fault pattern controls the trends of the submarine canyons, which have supplied up to a kilometer of probable Quaternary sediments to the San Lucas Fan system at the foot of the continental slope.

The La Paz fault is a major structural break at the western side of the Cape Region. Uplift of the region with associated normal faulting and strike-slip movement along the La Paz fault are related to formation of the Gulf as the continent overrode the East Pacific Rise since the late Miocene. The northern part of the Gulf appears to have opened in the late Miocene or early Pliocene, while the mouth did not open until late Pliocene.

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