SOUTHEAST COAST - THAILAND
This region covers Trat, Čhanthaburi, Rayong, and Southern Chonburi čhangwat. It is delimited on the north by hills and mountains along the southern edge of the Pračhin (Ban Pakong) River Valley, on the west and south by the Gulf of Thailand, and on the east by a line of flat-topped hills, the Banthat Range, which marks the Thailand-Cambodia border. The Southeast Coast region includes a well-dissected upland in the northern and central parts, and a coastal plain in the south and west. It is drained by numerous streams, most of which flow in a southerly direction. The principal rivers are the Čhanthaburi, Pra Sae, Wen, and Trat. There are a number of peaks in this region between 2,500 and 5,000 feet altitude.
The much indented coastline is fringed with rocky forested islands. The island of Sichang, lying near the northeast corner of the Gulf just off Siracha, forms a natural sheltered anchorage for large steamers unable to cross the bar at the mouth of the Čhaophraya River. The largest island along this coast is Chang, between Čhanthaburi and Trat. It has an area of about 70 square miles and a peak that rises nearly 3,000 feet above sea level. Just to the southeast is Kut, another sizeable hilly island. In the vicinity of the muddy estuaries of Pra Sae and Wen mangrove swamps abound. Elsewhere along the coast are many white sandy beaches.
Two important structural trends are noticeable in this region. Along the coast that faces the Bight of Bangkok (north of Cape Liant) there is a northsouth strike parallel to the Čhaophraya depression, the western edge of Khorat region, and the trend of the Central Cordillera. Along the southwest-facing coast (east of Cape Liant) there is a northwest-southeast strike, which is more or less parallel to the folded structures on the southwest edge of Khorat and in Cambodia. From southeast to northwest stretch the Cardamom Mountains of Cambodia, with peaks between 3,300 and 4,500 feet. The Banthat Range, which marks the present-day boundary between Thailand and Cambodia, and the Čhanthaburi Mountains, which reach an altitude of 5,400 feet, follow the same general direction.
In many places the arrangement and form of separate mountains and ranges reflect the geological structure of the region. In the region of Čhanthaburi the higher peaks, such as Khao Sabap and Khao Krat, are granitic batholiths. To the west of these mountains are wide plains in which isolated hills stand like islands. The outward forms of Khao Sabap and Khao Krat clearly reflect the occurrence of sedimentary formations about the granitic cores. A low, anticlinal fold with a granitic core determines the morphology. East of Rayong there are alluvial plains through which the foothills protrude. Separated mountains and ranges reach their greatest height in Khao Kiu, 2,300 feet. Visible for many miles, this peak is one of the landmarks for navigators in the inner part of the Thai Gulf and for the trip to Sichang Island. This is a sinking coast, and the numerous islands lying along it are peaks of a drowned landscape. All of them resemble the coastal areas.