The Mendanau Islands Geosite is one of the most striking natural landscapes in Belitong. Its rocky formations tell a story that dates back more than 270 million years. The island’s northern coast is lined with towering vertical rock walls, created from metasedimentary rocks of the Kelapakampit Formation, originally formed in the Permo-Carboniferous era (270–310 million years ago). What makes these formations unique is how they were once laid down in horizontal layers but later pushed upright by powerful geological forces.
This dramatic transformation is linked to the second tectonic orogeny event during the Mesozoic era, when rapid plate movements and horizontal pressure warped and folded the rocks, causing Belitong Island to re-emerge. Adding to this geological drama, the Tanjungpandan granite intruded into sandstone and claystone during the Upper Triassic–Jurassic period (200–270 million years ago). The result is a spectacular natural fortress—vertical walls of flysch metasedimentary rock that can be admired especially at Pulau Langer and Batu Dinding.
Beyond its geology, Mendanau is rich in biodiversity. Its forests are home to the Simpor plant, often seen as a magical symbol of resilience, and the protective Petaling tree. Wildlife includes the tiny yet graceful Pelanduk (mouse-deer) and the colorful Tusena, or Three-Colored Squirrel (Callosciurus prevostii), which is found only in this site.