The south-western portion is characterized by the low-lying hills with undulating and rolling terrain, having elevations ranging from 90–120 meters above mean sea level. These are basically shale and sandstone materials which dominate the Isabela-Kalinga boundary. The eastern edge, meanwhile forms part of the foothills of the major mountain range in the area and dominates the eastern flank of Quezon. This high relief area has peak elevations of up to 200 meters above mean sea level and is composed primarily of volcanic rocks.