The 51 islands of the park archipelago lie in the Andaman Sea from 20-70 km.. off the extreme southwest coast of peninsular Thailand. Tarutao, the largest of the islands, is 26.5 km. long and 11 km. wide. The topography is mostly mountainous (highest point 708 m.) with a few broad plains and valleys. Semi-evergreen rain-forest blankets about 60 percent of the island, and pure mangrove swamps are found in several areas. Long sandy beaches lie along the western coast from Pante Bay to Makham Bay, and at Talo Udang Bay in the south.
Tarutao is a Malay work meaning old, mysterious and primitive. Preliminary geological work has borne out the first of these adjectives. Much of Tarutao is composed of very old Cambrian sandstone. The northern and southeastern portions of the island consist of limestone rock. Most of the caves on the island are formed in limestone rock.
The Adang-Rawi group of islands lies about 50 km.. west of Tarutao and includes Adang, Rawi, Dong and Lipe. Adang Island. with a steep and rugged landscape almost completely covered by tropical rainforest, may be the most wild and appealing of the islands. Sparkling clear water and superb coral reefs provide habitat for a wide variety of marine life forms, including many brightly colored fish. Beautiful beaches consist of quartz derived from Adang's Cretaceous granite makeup and coral fragmants. Several waterfalls plummet down Adang's eastern slopes in times of heavy rain.