The major part of the municipal area is composed of Alluvium River Terraces which is particularly described as fluvicatile lacustrine alluvium composed of unsorted loosely consolidated pebbles, gravel, silt, coral debris and clay that can be found in flooded plains, riverbanks, sand bars, beaches, and tidal flats. It is notable that river terraces along the Lagonoy River and its tributaries which include also the Rangas River that practically originating from the foot of the Mount Isarog account for about 90.69% or 4,264.9826 hectares of the total land area of the municipality while the rest is of igneous and metamorphic rock origin of which volcanoclast alluvial fans cover about 0.19% or 8.94 hectares. These are specifically found in barangays Catalotoan and Salogon. Note that volcanoclast is a thick and extensive pyroclastic material consists of ashes, cinder lapili, tuff agromerate and volcanic debris while alluvial fans consists only of worked pyroclastics.