The Kiboriani Mountains, a western outlier of the Ukagurus, and East African Plateau lie to the west.

Rainfall is higher on the southern and eastern slopes, and lower in the mountains' rain shadow to the north and west.

[3] The Ukaguru Mountains, along with the others in the Eastern Arc, are made up of ancient crystalline Precambrian rocks that were uplifted over millions of years along fault lines.

[citation needed] The long-term persistence of a humid climate and the isolation of each mountain range has led to a great deal of endemism, and a very diverse flora and fauna.

[8] Tree species in the montane evergreen forests include Balthasaria schliebenii, Ocotea usambarensis, Podocarpus milanjianus, and Polyscias stuhlmannii.

Large areas of degraded montane grassland lie west of the main ridgeline.