Running through the middle of the peninsula are several mountain chains, with the highest elevation at Khao Luang, , in Nakhon Si Thammarat Province. Ranging from the Kra Isthmus to Phuket Island is the Phuket chain, which connects to the Tanao Si Mountain Range further north. Almost parallel to the Phuket chain, but to the east is the Nakhon Si Thammarat or Banthat chain, which begins with Samui Island, 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 up.