Paleomagnetic measurements of samples from the Mio-Pliocene Purisima Formation demonstrate that the Pomponio tectonic block of central coastal California has rotated clockwise by approximately 35¿ to 55¿ within the last 2.5 million years. The most likely interpretation of this data is that the Pomponio block is broken into several small blocks which have rotated by various amounts. The data suggest that rotations contribute to vertical deformation and secondary faulting within the central San Andreas Fault System, and that they play an importnt role in the accommodation of shear along the fault system. ¿ American Geophysical Union 1991