Geological field investigation in San lldefonso Peninsula, Northeastern Luzon reveals the presence of Late Mesozoic ophiolitic and volcanogenic basement rocks. Results from our structural analysis show that these genetically diverse rock units were juxtaposed prior to the installation of an Eocene magmatic arc. The Late Mesozoic and Eocene age rocks are in turn unconformably covered by a late Oligocene sedimentary sequence. Our field observations and new paleontological results lead us to propose a structural evolution of the San lldefonso Peninsula, taking into account the available data on the Northern Sierra Madre orogeny. The main structural events are: A) the obduction of the Dibut Bay Meta-ophiolite during the early late Cretaceous (~92 Ma), B) the regional metamorphism affecting the Late Cretaceous volcanic arc sequence from Paleocene to Early Eocene. C) the folding of the Eocene volcanic arc sequence contemporaneous with the uplift of the optiiolitic materials during the Early Oligocene (pre-late Oligocene) and D) the minor strike-slip movements along the Divilacan Fault Zone before the Middle Miocene.