Soils are of the frigid and cryic temperature regimes and support forests dominated by Pacific silver fir, western hemlock, mountain hemlock, Douglas fir, and noble fir. The Cascade Crest Montane Forest ecoregion consists of an undulating plateau punctuated by volcanic buttes and cones that reach a maximum elevation of about 6,500 feet. Its Pliocene and Pleistocene volcanics were glaciated leaving numerous lakes in their wake. The ecoregion is extensively forested with mountain hemlock and Pacific silver fir. Elevations range from 5,600 to 12,000 feet.
Active glaciation occurs on the highest volcanoes and decreases from north to south.
The winters are very cold and the growing season is extremely short. Flora and fauna adapted to high elevations include herbaceous and shrubby subalpine meadow vegetation and scattered patches of mountain hemlock, subalpine fir, and whitebark pine. The Umpqua Cascades ecoregion is a transitional zone between the lusher and moister forests of Ecoregions 4a and 4b to the north. Vegetation is a mix of grand fir, white fir, western hemlock, Pacific silver fir, and Douglas fir with Shasta red fir also occurring and increasing to the south. Vegetation diversity is greater than in Ecoregions 4a and 4b, which have cooler summers.