It consists of the catchment area of the Karamana River, which originates from Chemmunjimottai, the tallest hill within the sanctuary.

The sanctuary is named after the Peppara Dam, commissioned in 1983 to augment the drinking water supply to Thiruvananthapuram city and suburban areas.

The terrain is undulating with elevation ranging from 100 m to 1717 m. The area of the sanctuary is 75 km2 with tropical moist evergreen forests and myristica swamps.

The Peppara Wildlife Sanctuary is situated on Thiruvananthapuram-Ponmudi Road, about 50 km northeast of Thiruvananthapuram.

Common tree species are Terminalia paniculata, Terminalia bellirica, Pterocarpus marsupium, Palaquium ellipticum, Mesua ferrea, Hopea parviflora, Bombax ceiba, Syzygium cumini, Lagerstroemia microcarpa, Albizia procera, Alstonia scholaris, etc.