Unconformably overlying all formations in the Baguio district is the Klondyke Fm. Most workers agree that its age may be fixed as Late Miocene (Balce et al., 1980; Wolfe, 1988; Mitchell and Leach, 1991). The Klondyke Fm includes a wide range of lithologies and sedimentary facies, but most are clastic and almost entirely andesitic in composition. The other major lithologic unit in the district is the Agno Batholith; it is predominantly composed of hornblende quartz diorite. Radiometric dating indicates that the different rocks in the batholith were intruded in several phases.