Bohol's mainland exhibits the following salient physiographic units:
1. The east and west coast display northeast trending ranging up to 870 meters in elevation (Mt. Mayana) that drop steeply to the coast. These ranges reflect the major structural units of the island.
2. The central (Carmen area) and northern part of the island (Trinidad) are a vast expanse of relatively rolling plains and flatlands.
3. The development of beautifully-arranged, symmetrically formed "haycock hills" in Carmen-Batuan-Bilar-Balilihan area in the east central part of the island is suggestion of a well-defined system of shears and joints.
4. An elongated cluster of hills of moderate height lies in the northeastern part of the island (Ubay area).
5. An east-west ridge connects Alicia with Carmen.
6. The Anda Peninsula and Loon Peninsula strongly suggest elevated plateaus.
7. At least five different Plio-pleistocene terrace levels ranging in height from 10 to 300 meters have been etched both in Carmen sandstone and shales and Maribojoc limestone.
8. The drainage pattern is generally radial. The west is drained by the Abatan River (350 sq. km.) and Wahig-Inabanga Rivers (570 sq. km.); the north by Alog, Ipil (250 sq. km) and Soon Rivers; the east by the Mabini and Guindulman Rivers; and the south by the Loboc-Loay (160 sq. km.), Jagna and Garcia-Hernandez Rivers. These rivers are not important for navigation purpose.
9. The "Ilihan Plug" south of Tubigon with an elevation of 240 meters above sea level, presents a unique geomorphologic element. At a distance, this plug is suggestive of a limestone hill with white cliffy margins.
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