The mountain around Khao Sam Roi Yot National Park are mostly limestone, which have been formed from sediment originating from the ocean bed.
Over thousands of years the earth crust has moved and pushed up stone to become the Limestone Mountains. Limestone is soft and disintegrates easily from water.
Limestone Mounatins are craggy, so flowing water causes holes and caves. Due to this natural factor, Khao Sam Roi Yot National Park has many such as Phraya Nakhon Cave.