Area: 102.36 hectares.
Within the Dartmoor Environmentally Sensitive Area.
The site lies on the steep slopes and valley floors of the River Walkham and the River Tavy at an altitude of between 50 and 150 m. It has developed on soils derived mainly from slates of the Upper Devonian age which in some areas have been disturbed by past mining activities.
Grenofen Wood supports a diverse lichen flora which includes a number of uncommon and rare species. Over 80 species of lichen have been recorded in Grenofen Wood which is one of the very few sites in Great Britain for the rare oceanic lichen Parmelia horescens, and one of two localities in southern England for Cetrelia cetrarioides. Other species of note include the rare Desmatina quercus with Cladonia ochrochlora and Dimerella diluta all being uncommon in the south-west.
West Downs is an acidic grassland on a south-facing slope dominated by bracken Pteridium aquilinum, which supports nationally important populations of the declining high brown fritillary butterfly Argynnis adippe. Violets Viola spp., the larval foodplant, grows abundantly beneath the bracken canopy. Other species of note include the nationally scarce pearl-bordered fritillary Boloria euphrosyne.
The woodland valley slopes are dominated by both pedunculate oak Quercus robur and sessile oak Quercus petraea with occasional silver birch Betula pendula, rowan Sorbus aucuparia, hazel Corylus avellana and holly Ilex aquifolium over a ground flora characterised by an abundance of bracken, bramble Rubus fruticosus, bilberry Vaccinium myrtillus and mosses. On the flatter slopes beside the river, alder Alnus glutinosa and alder buckthorn Frangula alnus are common, while, locally, wet flushes support extensive colonies of opposite-leaved golden saxifrage Chrysosplenium oppositifolium.
The site supports a breeding bird community representative of western oak woods, with dipper Cinclus cinclus and grey wagtail Motacilla cinerea breeding beside the River Walkham. The river is also used by otters Lutra lutra.