We will use 2 arrays of seismic instruments to record fault-zone guided waves generated by earthquakes along the San Andreas Fault system in San Gorgonio Pass, California. In particular, we hope to determine if guided waves may be transmitted through the intersection of the San Bernardino strand of the San Andreas Fault and the San Gorgonio Pass Thrust Fault. If so, this result would imply a through-going wave guide, and thus a through-going fault structure that might in turn support through-going earthquake rupture in this region. Through-going rupture would have important implications for earthquake magnitude, ground motion, and overall seismic hazard in Southern California.