300 million years ago, Khao Sok was merely a muddy deposit of pebbles and sandstone at the bottom of a great river, but a lot has changed. As sea levels rose, Khao Sok became part of a massive coral reef stretching from China to Borneo. Geological activity then thrust this area upward to form the massive limestone mountains, also known as karsts. The last 60 million years has seen the evolution of an evergreen tropical forest that is now older and more diverse than the Amazon.