Topographically, Sri Lanka is divided into three morphological areas and  Sinharaja belongs to the middle elevational range or the "uplands" which has a height range of 270 to 1,060 meters and a slope range of 10⁰ to 35⁰. The forest is located on the Rakwana massif which lies detached from the main central massif of the island.

Peaks of Sinharaja - view from Sinharaja

                    The Sinharaja area consists a series of parallel strike ridges valleys. In the eastern part of the forest ,the ridges have an east-west trend while in the western part, the ridges have a northwestern to south-eastern trend. From north to south, the decrease in elevation is gradual while form east to west, the decrease is quite marked (1,100 to 300) meters). There are several prominent peaks in the eastern sector of the Reserve which includes the 1,171 meters high Hinipitigala Peak, the height peak in the Reserve. From this height the altitude often drops down to 90 meters in the valleys (Figure 4).

Figure 4 Prominent peaks in the Sinharaja area (Survey Department -Rakwana sheet, 1973)

                     A large number of streams arise in the Sinharaja region and drainage occurs in a rectangular "trellis" pattern. The streams on the southern side form the headwaters of the Gin Ganga while those on the Kukulu Ganga, a major tributary of the Kalu Ganga (Figure 5). 

Figure 5.    Drainage map of Sinharaja   (adapted from Merrit and Ranatunga, 1959)