[2] Usun Apau is a volcanic plateau covering an area of approximately 1,550 km2, and averaging 1000 meters in elevation.

The northern, eastern, and western edges of the plateau end in steep escarpments nearly 300 meters high.

[2] The plateau is covered by montane rain forests, including kerapa, a stunted forest of small trees with gnarled trunks and which forms on poor soil with bad drainage, and kerangas forest, made up of tall trees with thin trunks growing on infertile volcanic soil.

[3] The plateau is home to several vulnerable and near-threatened bird species, including the Bulwer's pheasant (Lophura bulweri), Bornean ground cuckoo (Carpococcyx radiceus), rhinoceros hornbill (Buceros rhinoceros), ferruginous partridge (Caloperdix oculeus), Dulit frogmouth (Batrachostomus harterti), Gould's frogmouth (Batrachostomus stellatus), Whitehead's trogon (Harpactes whiteheadi), Hose's broadbill (Calyptomena hosii), black oriole (Oriolus hosii), Sunda laughingthrush (Garrulax palliatus), and Everett's thrush (Zoothera everetti).

[2] In August 2022, Sarawak's premier Abang Abdul Rahman Johari Abang Openg announced that the Government of Sarawak would improve road access to the national park, and Julan Waterfall in particular, to open it to tourism, as part of the state's Post-COVID-19 Development Strategy through 2030.