Based on geological history, Mount Halimun and neighbouring peaks are sisters of South Sumatra's Barisan Mountains. During the Lower Miocene and Pliocene (10-20 million years ago) the rocks of the whole area were pushed upwards. This uplifting formed the Bayah Dome. Subsequent partial collapse of the structure resulted in the area of lowland, which now forms the Sunda Straits separating Java and Sumatra. The two islands were last linked some 10,000 years ago.

Accompanying early tectonic movements, lava ridges built up along fracture lines in the earth's crust. With dome collapse, a south facing horseshoe formation of volcanoes developed. Over the year weathering has eroded the area, giving a more rounded landscape, but these ancient features remain.

Mount Halimun's rocks largerly consist of breccia and andesitic and basalt lavas. There alsoa

s few sedimentary areas. Gold and silver ores occur, mining taking place in the west and southwest.