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

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

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

[8] Miombo woodland covers the Mkata-Wami plain to the east, and the low hills to the south, west, and north.

At lower elevations on the eastern slope, evergreen lowland rainforests dominate, with flora similar to the humid Zanzibar-Inhambane coastal forests further east.

Montane rainforests predominate between 1400 and 2000 meters on the eastern slope, with mossy cloud forests at higher elevations.

[13] The Mkingu Nature Reserve is home to one of Tanzania's largest remaining undisturbed areas of montane forest.

[15] The Kanga South CFR (6,664 ha) is in the northeastern portion of the mountains, divided from the main block by the Mjonga River valley.