A MS=6.5 earthquake occurred on 8 July, 1975 in the northern part of the Gulf of California. The calculated seismic moment is 2¿1025 dyne-cm. This event occurred in a region of particular interest since the position of the transform fault in this region was not well known and had been locked for at least 20 years. Over 180 aftershocks were located along a zone 54 Km long, 10 Km wide and 10--15 Km deep running between Baja California and Isla Angel de la Guarda. The depth of the aftershock zone is somewhat greater than that found in previous studies in the Gulf. The aftershock trend and that of the fault plane solution is consistent with an event occurring along a vertical strike-slip fault with motion in the direction of known regional plate movement. ¿ 1977 American Geophysical Union