Measurements of magnetic fields along the San Andreas fault indicate that inhomogeneous tidally generated current systems flow in and around the fault system. These currents limit measurements of short-term local fields of tectonomagnetic origin to about 0.3 nT but can be easily removed. Ocean-tidal induction into a complex fault zone with higher than average electrical conductivity appears to be a more likely explanation than either piezo-magnetic effects due to solid-earth tides or ionospheric-tidal induction. The amplitudes of the induced diurnal harmonics decrease fairly linearly to the southeast along the fault. This result is consistent with expectations from a hotter and more conductive crust and upper mantle in southern California, as indicated by heat-flow data for this region.