Ko Pha-ngan, and Ko Tao in Surat Thani Province and ends at the Malaysian border at the Ko Ta Ru Tao archipelago. The border with Malaysia is formed by the Sankalakhiri range, sometimes sub-divided into the Pattani, Taluban, and Songkhla chain. At the Malaysian border, the Titiwangsa chain rises.

The limestone of the west coast has been