The chain runs from northeast to southwest, with the Taita Hills being in Kenya and the other ranges being in Tanzania.

They are delimited on the southwest by the fault complex represented by the Makambako Gap that separates them from the Kipengere Range.

During a period some 10 million years ago, when the climate was cooler and drier, the lowland forests were converted to savanna, leaving the mountain ranges as "islands" where the tropical forests continued to flourish, fed by moisture-laden winds from the Indian Ocean.

This isolation of each mountain range has led to a great deal of endemism, and a very diverse flora and fauna.

Four of the endemic birds are similar to Asian species, and may have evolved at a time when the Arabian Peninsula had a coastal fringe of vegetation to act as a passageway; the Udzungwa forest partridge (Xenoperdix udzungwensis) is a relict and example of this, it is found only on the Rubeho Mountains and Udzungwa Mountains, and its closest relatives appear to be the hill partridges of Asia.