Bilauktaung Range, mountain chain in southeastern Myanmar (formerly known as Burma), defining part of the country’s border with Thailand. The range, which runs northeast to southwest, is also known as the Tenasserim or Tavois mountains. It begins at Three Pagodas Pass, about midway between the city of Moulmein and the town of Tavoy, and extends southward for 400 km (250 mi) before dropping off sharply to the Andaman Sea. The highest elevations are at Ngayanni Kyauk Taung (1,531 m/5,023 ft) and Palan Taung (1,455 m/4,774 ft). The steep descent to the Andaman Sea creates a narrow coastal plain that is widest near the town of Mergui. The central spine of the Bilauktaung Range is made up of granite and granodiorite (granite and quartz-containing diorite) dating from the Cretaceous Period, 136 million to 65 million years ago. Sandstone rocks are also found in some areas. The mountains are heavily forested.