The mountains are made up of proterozoic rocks, including schist and marble, of the Mozambique Belt.

The Mahenge Mountains are covered with evergreen forest, miombo woodland, grassland, and heathland.

[1] The lower elevations of the mountains and surrounding plains are covered in deciduous miombo forests and woodlands.

An analysis of satellite images taken between 1999 and 2003 found 19 km2 of the mountains were still covered in evergreen forest.

[1] Water is generally scarce due to the limestone plateau, but despite this the area gives its name to the Mahenge Toad (Mertensophryne loveridgei).

Sali Forest Reserve, established in 1954, preserves 1890 ha between 1050 and 1500 meters elevation.