The tectonic evolution of southeastern Mexico has been a subject of major controversy, not only in regard to past geometry but also in the timing of proposed eological events as well. For the past 10 years, most, if not all, investigators agree that the Gulf of Mexico Basin was formed by Late Jurassic time and that the Maya Terrane was in its current location prior to the Cretaceous. In order to gain further insight into the drift history of the Maya Terrane we have undertaken a kpaleomagnetic study of the uppermost Jurassic-Lower Cretaceiys (Tithonian-lower Neocomian) San Ricardo Formation in southeastern Mexico, at 93.7 ΔW, 16.8 ΔN. The sampling site is located east of the Isthmu of tehuantepec, on the southwest side of the Maya block, at the base of the Yucatan Peninsula. A suite of 133 samples was collected ins tratigraphic succession from a 114-m-thick sequence of red shales and sandstones near Cintalapa, Chiapas, Mexico. After progressive thermal demagnetizaton of all samples at six steps rom 350 ¿ to 630 ¿C, 89 samples were selected for final paleopole analysis on the basis of their magnetic stability. Four different polarity intervals were observed, the sequence being from bottom to top; N, R, N, R which assists in the assessement of the reliability of the observations. The mean pole position obtained, 160.0 ¿E, 69.8 ¿N, agrees with the mean pole position of the upper part of the Morrison Formation of Colorado, a unit of virtually identical age. These results indicate that no discernible rotation or displacement of the Maya block has occurred since at least early Neocomian times. ¿ American Geophysical Union 1990