The range extends east of the Salween until almost reaching the Golden Triangle area, separating the Salween watershed from the Mekong watershed. At its southern end the Thanon Thong Chai Range subrange stretches further southwards into Thailand between the Sai River in the east and the Pai River in the west; the latter separating the Daen Lao from the Thanon Thong Chai Range.Some geographers include the Thanon Thong Chai Range subrange as part of the Daen Lao Range.The Khun Tan Range also extends southwards from the Daen Lao Range, parallel to the Thanon Thong Chai mountains, but it differs geologically and structurally from the latter.