We present paleomagnetic data for Cretaceous sedimentary rocks from the El Rosario formation of northwestern Baja California which imply a northward displacement of 15.0¿3.8¿ and a 30.8¿4.2¿ clockwise rotation for the Baja Peninsula relative to the North American craton since late Cretaceous time. Paired IRM acquisition, X-ray diffraction, and M¿ssbauer spectra indicate that finite--grained magnetite is the dominant magnetic mineral present, with goethite and other more oxidized phases rare to absent. Biochemical evidence constrains the amount of diagenesis undergone by the sediments. We subjected oriented samples to both progressive alternating field and thermal demagnetization, and in general found univectorial magnetizations, yielding a mean inclination of 44.6¿ and declination of 5.3¿ with an α95 of 2.0¿. The corresponding paleolatitude for these values is 26.3¿1.6¿. Most of the samples were of normal polarity, which is consistent with their deposition with the upper Campanian chron 33N. We collected samples from younger Maastrichtian sediments which yield consistent, reversed directions. ¿ American Geophysical Union 1989