Sir Joseph Dalton Hooker had advised the British Government to leave all Montane Forests above 5000 ft. undisturbed and an administrative order to this effect had been issued in 1873 that prevented clearing and felling of forests in the region. Horton Plains was designated as a wildlife sanctuary on 5 December 1969, and because of its biodiversity value, was elevated to a national park on 18 March 1988. The Peak Wilderness Sanctuary which lies in west is contiguous with the park. The land area covered by Horton Plains is . Horton Plains contains the most extensive area of cloud forest still existing in Sri Lanka. On July 2010, the Central Highlands of Sri Lanka which incorporates Horton Plains National Park, Peak Wilderness Sanctuary and Knuckles Mountain Range was inscribed on the World Heritage List.