The Nimba Range forms part of the southern extent of the Guinea Highlands, adjacent to the Toura Mountains.

It is composed mostly of Precambrian rock, including granite and quartzite which contain deposits of iron ore.[2] Mining of top-quality iron-ore poses the major threat to the unique geomorphology and wildlife.

Other rare and endangered animals are West African lion, pygmy hippopotamus, zebra duiker, and western chimpanzee that uses stones as tools.

The Nimba Range is a part of a distinct freshwater ecoregion with a high portion of endemic aquatic species.

[2] The endemic frog species Nimbaphrynoides occidentalis, which inhabits the montane grasslands of the range, is totally viviparous.

[6] Ptychadena submascareniensis is another frog species that has been found only on Mount Nimba and in the Loma Mountains of Sierra Leone.

Lower montane forests of Lophira procera, Tarrietia utilis, Mapania spp., Chlorophora regia, Morus mesozygia, and Terminalia ivorensis occur between 600 and 900 meters elevation.

Swift-running streams descend steep slopes of the range, and often experience torrential floods during the rainy season.

The Nimba Range's high elevation, its rapids and waterfalls that isolate habitat areas, and the stability of the aquatic environment, have promoted speciation.