The park lies between the Polonnaruwa-Batticaloa road and Mahiyangana-Padiyathalawa road in the districts of Ampara, Badulla and Polonnaruwa and spans the border between Eastern and Uva provinces.

Degradation of the pre-Cambrain rock has resulted in the formation of a mature mantle and undulating peneplain, broken by a number of prominent remnants of erosion (rock outcrops and ridges).

The topographic feature is the 8 km long range of Rocky Mountains in the south west of the park. The area of park is 58,7850 ha. The park was extended in the east from its original size of 51,468 ha on September 16, 1985 to provide additional habitat for wildlife and to ensure protection of the immediate catchments of the NDK reservoir.

Conditions are influenced largely by the north-east monsoon, or Maha which lasts from October to late January. The mean annual rainfall is 1,650 mm. Annual evapotranspiration rates normally exceed precipitation levels and mean annual temperature is about 27 °C.

The park is located entirely within the Dry Zone, although its southern edge borders on the intermediate zone.

The climax community of the area is tropical evergreen forest. The rare and endemic tree , the vatica obscura, the only species of the Dipterocapaceae to occur in the Dry Zone, is found in a restricted location on the banks of the Maduru Oya and Gallodai Aru.