The Kelabit Highlands is thought to developed from the rifted continental crust where water sediments were deposited before Borneo was separated from the mainland Eurasian plate. This is evidenced by the presence of evaporite and limestone found in the area. Evidence of folding and faulting along the NE-SW axis is also found in this area. The types of stones changes from oxidised iron and coal-bearing sandstones in the east of Kelabit highlands, to mudstone and limestone of the Kelabit highlands, and grey sandsones westwards in the Mount Murud region. Pulong Tau National Park covers the water catchment area of Baram, Belait, Limbang, Tutong, Trusan, and Padas rivers.