There are two halves to this region: The Washpool and the Spirabo
The geology of the Washpool half of the wilderness is dominated by middle to upper Permian volcanics and intrusives, including the Coombadjah Volcanic Complex and Stanthorpe Adamellite. The Gibraltar Range, along which the Washpool region lies, is an easterly outlier of the New England Tableland and is a plateau-like land form dissected by numerous deep valleys leading to the Rocky (Timbarra) River in the west and to Washpool Creek in the east.
The Spirabo half of the wilderness to the west consists mainly of Devonian metamorphosed mudstones and sandstones comprising argillites, phyllites and slates. The soils of the wilderness are typically yellow podsols of only fair fertility which are very prone to gully erosion.
The Washpool Wilderness includes two identified wild and scenic river systems, the Timbarra (Rocky) River and Washpool Creek and its tributaries.
The vegetation of the western and eastern halves of the wilderness differ considerably. The Washpool half features rainforest and moist open forest, while the Spirabo region features dry schlerophyll with patches of rainforest refugia in favourable niches.
The Washpool half of the wilderness nomination to the east contains the important warm temperate rainforest association Coachwood-Crabapple-Corkwood (Ceratopetalum apetulum-Schizomeria ovata-Caldcluvia paniculata). This area, also referred to as Willowie Scrub, is the largest stand of unlogged Coachwood in the world. Coachwood is also found growing in association with another warm temperate rainforest species, Yellow Carrabeen (Sloanea woolsii). Sub-tropical rainforests grow in isolated pockets in moist gullies with deep soils, while lowland sub-tropical stands are found on the south side of Coombadjah Creek. Dry rainforest is found in the lower and middle reaches of Washpool Creek. Wet sclerophyll forests of New England Blackbutt (Eucalyptus andrewsii) grow on higher slopes, often with a rainforest understorey, giving way to Tallowwood-Blue Gum-Brush Box associations (E. microcorys-E. saligna-Tristania conferta) further down. Dry sclerophyll forests, again of New England Blackbutt, are found on high western slopes, whereas eastern slopes are predominantly of Spotted Gum (E. maculata). Dry open forests of Red Bloodwood (E. gummifera), Mountain Gum (E. dalrympleana), Blackbutt (E. pilularis), Narrow-leaved Peppermint (E. radiata) and Forest Oak (Casuarina torulosa) are found on fire-prone, dry slopes. Some natural grasslands are found to the south of the area, which in summer months are covered with Christmas Bells (Blandfordia nobilis).
The Spirabo region of the Washpool Wilderness contains most of the remaining forests of the New England Tableland region. These forests have been extensively cleared for agriculture. The state-wide summary of forestry regions prepared by the New South Wales Pulp and Paper Industry Task Force Report (Department of State Development, 1989) showed that the Glen Innes region has by far the lowest percentage of forested lands protected in national parks, with only 4% of its forests being reserved. Several inadequately conserved plant associations are found in the area.
Washpool wilderness is part of a broad, virtually unbroken belt of mostly undisturbed forested land extending north to south along the eastern escarpment and plateau margins from Ebor to the Queensland border. Thus, it forms one of the largest significant refuges for forest dependent fauna in the north-east part of the state. Several species listed in the Threatened Species Conservation Act 1995 are known to occur in the forests of the western sector of the area. These include six mammals (Yellow-bellied Glider, Tiger Quoll, Rufous Bettong, Great Pipistrelle, Golden-tipped Bat and Greater Broad-nosed Bat), two birds (Glossy Black Cockatoo and Sooty Owl) and one amphibian (Litoria subglandulosa). Several other threatened species are expected to occur in the area. These include seven species of mammal (Koala, Brush-tailed Phascogale, Squirrel Glider, Hastings River Mouse, Brush-tailed Rock Wallaby, Common Bent-winged Bat, Large-footed Mouse-eared Bat and White-striped Mastiff Bat) and one reptile (Carpet/Diamond python). The threatened fish, the Eastern Freshwater Cod, is expected to occur in the river systems of the area.
Animals recorded in the North Washpool portion of the wilderness include twelve amphibian species, 31 reptile species, 122 bird species and 52 mammals species. The threatened fauna found or expected to be found in this area include seven mammals, six birds, two lizards and three frogs.