The rocks there are made up of sandstones. The beach Telok Assam shows many features of wave action. 75 million years ago, the area that is now in the park was submerged in the sea. Due to tectonic movement, intense folding and faulting occured which resulted in the uplifting of land. The result is Bako Plateau with steep cliffs on its edges.
Active erosion takes place all the time.
Strong waves erode the base of the cliff between the high tide and low tide level. This zone is called the zone of active erosion. This action is called undercutting. Undercutting by the waves causes notches to enlarge. Slumping occurs when the overhang loses support of the rocks beneath.