Detailed geographic mapping conducted within the area revealed the presence of metamorphosed gabbros1 as basement rock of Labason. It is megascopically described as generally dark, greenish gray to very dark gray, medium coarse-grained, foliated, granular, with occasional lenses of quartz. Outcrops of this rock type are abundant in the immediate vicinity of Mount Dansalan. This rock unit is believed to be a part of the Pre-Tertiary Tunguauan Schists2 of Santos-Ynigo (1953) which was later mapped as Pre-Jurassic Granites (PBM, 1964) and named Dansalan Metamorphics (Querubin et. al, 1968) due to its type of locality..
Tungauan Schists is uncomfortably overlain by uplifted gravel deposit and coral reefs. Occurrences of this lithologic unit evident along the lowlying hills of Mount Dansalan and within surrounding barangay of Labason. The exposed gravel was megascopically described as gravelly sand with abundance of rounded to subrounded, pebble to cobble size clasts of quartz and metamorphic rocks.