In the short historical record of northern Baja California, the largest earthquake has a magnitude 7.1. Most of the earthquakes with M_L > 6.0 occur along the Cerro Prieto, Imperial, and San Miguel faults; no significant seismicity is known to have occurred along the Agua Blanca fault. A large part of the microseismicity (M_L < 3.0) is sporadic, dominated by swarms, and in good correlation with mapped faults. Seismogenic depths are restricted to the upper part of the crust. Two seismic zones are defined by the microseismicity of the Mexicali-Imperial Valley; this activity is mostly clustered in the basement. Typical focal mechanisms are consistent with a strike-slip, right-lateral motion, striking northwest. This is the case for the last four eve ts of M_L > 6.0 in the Salton Trough. Focal mechanisms for the seismic zones and the head of the Gulf of California are mainly of a strike-slip and dip-slip nature.