Reconnaissance ground magnetic and gravity surveys were conducted in the southern portion of the Zambales Ophiolite Complex. Work of this nature was undertaken with the end in view of defining the boundary between the Cabangan and San Antonio Massifs of this ophiolite suite. Results obtained from the combined reconnaissance magnetic and gravity surveys delineate a structural feature which is believed to correspond to the Subic Bay Fault Zone. The SBFZ is proposed to be the structural boundary between the Cabangan and San Antonio Massifs.