Bahorok is only a small part of the 12.094.962 hectare of Mt.Leuser National Park. The magnificient rainforest of the park have become famous throughout the world as the harbor some of the most endangered and rare species on earth for example Sumateran Rhinoceros, Orangutan, and Rafflesia, the largest flower in the world. The park is inhabited by animals like the Great Argus Pheasant, Elephant, Sumatra Tiger, And as many as sevene species of primate, one of which is Siamang, which has an impressive, far-reaching vocal display. The agile and pretty face Thomas leaf-monkey and long tailed macaques are also commonly seen.
In total the park lists 285 species of bird, 90 of mammals, reptiles and 35 of amphibians.The park-flora contains some 3500 plant species and on each hectare of the low land forest you cana find amazing 60-13 tree species.
Geologically there are several limestone formation along the foothills of the mountains, some with the beautiful caves.Long ago these were coral reefs which have since been uplifted from the sea at rate of few millimeters per year by the processof colliding ocean floorsand drifting continens. These infinitely slow collision and the enormous forces involved have led to the formation of high mountain and volcanic zones. Only some 1800 years ago,during glacial somes.
The peaks of the park, Mt.Leuser, Mt. Kemiri and others, were still covered by glaciers snow and ice, sea level at that time was more than 80 m lower than at present and the island of Sumatera, Java, and Borneo then formed one huge land mass which has connected via Malaysia to the Asian mainland.