This chapter summarizes Mesozoic and Cenozoic paleomagnetic data from southern and Baja California that document significant latitudinal and rotational displacements of large-scale blocks within this region. Much of the displacement is associated with two large allochthonous terranes--the Santa Lucia allochthon and the Peninsular Ranges terrane--that accreted to the North American craton during the Tertiary. The Santa Lucia allochthon amalgamated at equatorial paleolatitudes during the Mesozoic, traveled northward relative to North America between 70 and 50 Ma, and accreted to North America in the Eocene. The Peninsular Ranges terrane amalgamated along the western margin of southern Mexico and Central America during the Mesozoic and early Tertiary, traveled northward rela ive to North America some time after 40 Ma, and accreted to North America and the Santa Lucia allochthon by the early Miocene. The suture zone between the Peninsular Ranges terrane and the Santa Lucia allochthon is marked by 90° clockwise rotations of structural blocks within these terranes. Other structural blocks in southern California have also been rotated, either as part of the tectonic processes associated with terrane accretion, or as part of later regional extension and right-lateral strike-slip motion along southern California faults.