Fourteen new fault plane solutions were determined for earthquakes in the Gulf of California and Rivera fracture zone regions. Four solutions in the Gulf corroborate previous work showing that right-lateral, strike-slip faulting on northwesterly trending planes is the dominant sense of slip. Three events near the southern part of Baja California reflect internal deformation of the Pacific plate; the sense of motion is not parallel to that in the Gulf. Solutions on the Rivera fracture zone are consistent with right-lateral, strike-slip motion on west-northwesterly trending faults. The measured sense of motion is also not parallel to that in the Gulf. These data demonstrate the existence of the Rivera plate as separate from the North American plate.