Then, in the Permian period, there was a transition from marine to terrestrial deposits in the area as the Uncompahgre Highland was uplifted to the north.

[4][5] Along Indian Trail Ridge, the highest terrain in the wilderness, the Paleozoic sediments are capped by younger Jurassic sedimentary rocks of the Dolores Formation.

[4][5] Noticeably lacking in the wilderness are volcanic lavas, tuffs, and conglomerates common in other areas of the San Juan Mountains.

While the wilderness has experienced repeated disturbances through the years, one third of the spruce-fir forests here are old growth stands that have avoided decimating fires, disease, insect outbreaks, and logging for centuries.

Significant stands of aspen occur in the wilderness on historically disturbed sites in both the subalpine and montane zones.

Alpine tundra, dominated by grasses and forbs, is limited to only the highest elevations of Indian Trail Ridge along the western margin of the wilderness.