The Tana River Primate Reserve, known to the locals as Mchelelo, was formed to protect two endangered species of monkey; the crested mangabey and the Tana River red colobus. It is one of the last remaining relics of the once massive Central African Lowland Rainforest, which became isolated from the rest of the forest during the seismic eruptions that caused the formation of the Rift Valley. As a result, much of the reserve's flora and fauna are uncommon to East Africa and bear traces of ancient links to the Congo Basin forests of the Miocene period.