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[1] A wide region in the central part of the Sierra Madre del Sur (SMS), southern Mexico, records two deformational phases between the Late Cretaceous and early Tertiary. The first is a progressive approximately E-W shortening phase that spans from the Coniacian to earliest Paleocene and involves deformation of Cretaceous marine sedimentary units. The second phase corresponds to Paleocene to early Eocene deformation that also affects continental sediments and is characterized by gentle folding and counter-clockwise rotation of previous shortening structures associated with strike-slip faulting. Here we present geologic, geochronologic, and structural data of two key areas of the Sierra Madre del Sur, the Guerrero-Morelos Platform (GMP), and the Huajuapan-Tamazulapan area in western Oaxaca to describe the geometry, kinematics, and timing of the Late Cretaceous and early Tertiary deformation. Two regional magmatic episodes constrain the deformational history: (1) the first between the Maastrichtian and the Paleocene (68-57 Ma) documents the end of Late Cretaceous shortening in the GMP; and (2) the second between the late Eocene and early Oligocene (37-29 Ma) has a more regional distribution. The time and space analysis of deformation and magmatism in southern Mexico led us to exclude flat subduction or collision of the Guerrero terrane to the west as the cause for Late Cretaceous shortening in the GMP. Considering the similarity in the time and style of deformation with that of the northern Chortis block, we favor an interpretation in which the tectonic evolution of the central and eastern SMS is the result of progressive interaction of the Caribbean plate with the southernmost edge of North America since the Late Cretaceous. doi: 10.1029/2006TC001981.