Trusmadi's geology tells a story older than the forest that covers it. The mountain is built from tertiary formations of mudstone, shale, and argillite, with beds of quartzite, sandstone, siltstone, and limestone breccia layered beneath. These are ancient seabed sediments, lifted and folded over millions of years into the peaks of the Crocker Range. The mountain sits within Crocker Range National Park, which covers 184,527 hectares of protected terrain. At its upper elevations, the forest transitions from lowland dipterocarp to mossy montane, where the trees shrink, the moss thickens, and the air turns cool and perpetually damp.

Trusmadi's cloud forest harbors botanical treasures found nowhere else. Nepenthes macrophylla, a species of pitcher plant, grows on the mountain's upper slopes, its enormous pitchers trapping insects in pools of digestive fluid. Even more remarkable is Nepenthes x trusmadiensis, a natural hybrid named for the mountain itself, a living testament to the evolutionary experiments that play out in isolation on tropical peaks. In 1999, the Sabah Museum and Louisiana State University Museum of Natural Science conducted a joint biodiversity expedition on the mountain, documenting species that had never been catalogued. The mountain is a laboratory of endemism, where altitude and isolation have produced organisms that exist on this single peak and nowhere else.

Since the COVID-19 pandemic, Trusmadi has emerged as one of Borneo's premier birdwatching destinations. Bird hides constructed on the mountain attract photographers and naturalists from across Southeast Asia, drawn by the chance to observe Bulwer's pheasant, one of Borneo's most elusive and spectacular birds. Trusmadi is one of only a few locations where this shy species has been reliably photographed, alongside Maliau Basin and the Jungle Girl Entomology Camp. Approximately 43 bird species have been recorded around the hides, with six to fifteen regularly visible for photography. The mountain has transformed from a niche climbing destination into a biodiversity tourism draw, bringing economic benefit to the surrounding communities of Tambunan and Keningau.

Three trails lead to Trusmadi's summit, each from a different direction. Wayaan Kaingaran approaches from Tambunan, Wayaan Mastan from Keningau, and Wayaan Mannan from Sinua in Sook, Keningau. The first two require four-wheel drive vehicles to reach their starting points, bouncing along logging roads and unpaved tracks that become treacherous in rain. Only Wayaan Mannan has a proper access road. The climb itself is demanding regardless of route, pushing through leech-filled lower forest into the stunted, wind-sculpted trees of the summit zone. Those who reach the top on a clear morning are rewarded with views across the Crocker Range and, on the best days, a glimpse of Mount Kinabalu's distinctive granite profile rising to the north.