The site is a small isolated limestone mountain as steep side cliff tower. It is in a public area with a water pond in the north and west. The southern side is a decorated landscape surrounded by four-meter wide concrete road. It covers an area about 20 acres. Khao Thanan is characterized as a karst topography with sea caves and sea notch indicating it was an islet off the coast. After that the sea level has been regressed leaving the islet as a small isolated mountain. The limestone is massive, pale grey, and fossiliferous. The fossils include bivalves, brachiopods, bryozoans, corals, sponges, gastropods and crinoids. The limestone was formed under shallow sea as a coral reef during probable Permian.