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The Usambaras are approximately 90 kilometres (56 mi) long and ranging from 30–50 kilometres (19–31 mi) in width. They are part of the Eastern Arc Mountains, which stretch from Kenya through Tanzania. The range is one of the world’s Biodiversity hotspots.
The range is accessible from the towns of Lushoto in the west, and Amani in the east. The Usambaras are commonly split into two sub-ranges, the West Usambara Mountains and the East Usambara Mountains. The East Usambara are closer to the coast, receive more rainfall, and are significantly smaller than the West Usambara.
The mountain range was formed nearly two billion years ago. Due to a lack of glaciations and a relatively consistent climate, the rainforest has gone through a long term and unique evolution resulting in an impressive amount of endemism and an old growth cloud rainforests. 
The West and East Usambaras are large ranges of Precambrian metamorphic geologic formations of acid-gneisses, pyroxenes, and amphiboles. These mountains were formed by faulting and uplifting creating the drainage system of troughs that form many watersheds, which provide water to a majority of the population of northeast Tanzania. 
The Usambara Mountains are fairly unique in East Africa with their natural regions still covered in tropical forests, which otherwise continentally remain primarily in Western Africa. Considered tremendously significant ecologically and a Biodiversity hotspot. There are many protected zones throughout the range, which are being expanded and contributed to by the Tanzanian government, associated NGO's and research teams, and donor countries such as Norway.
Several species are endemic to the Usambara forests, including the Usambara Eagle-owl (Bubo vosseleri), the Usambara Akalat (Sheppardia montana), the Usambara Weaver (Ploceus nicolli), the African violet (Saintpaulia ionantha), the tree species Calodendrum eickii.
A Shambaa kingdom based on Vugu was founded by Mbegha in the first half of the 18th century.  His grandson Kinyashi Muanga Ike gave the kingdom a stronger political and military structure. Under Kinyashi's son Kimweri ye Nyumbai the kingdom grew to cover both the west and east Usambaras, extending down to the coast and into the Pangani River valley to the south.  After Kimweri died in 1862 the kingdom fell apart in a succession struggle.  
In the late 19th century when within the Usambara District of German East Africa, German colonialists came into the area bringing with them a mix of cash crops like lumber trees, coffee, tea, and quinine, and also designated forests as reserves for either water conservation or timber use.  They also brought many new Western concepts, which often were diametrically opposed to traditional beliefs, such as coexistence with the forest versus forest as a "separate wilderness".  The result of colonialism was a massive change in the way forests were perceived in the community, and conversion of traditional agriculture to cultivating cash crops such as quinine, pine trees, bananas, maize, tea, and coffee.
In 1882 Adalbert Emil Walter Redliffe le Tanneux von St. Paul-Ilaire (know as Baron Walter), the Governor of the Usambara District of German East Africa, collected seed and plants of a small herb which were sent to Hermann Wendland, Director of the Berlin Royal Botanic Garden. Wendland cultivated the plants and recognized them as representing a new species in a new genus, Saintpaulia ionantha, with the English common name African violet. In the generic name. Saintpaulia he recognized von St. Paul-Ilaire; the specific name he assigned means violet (Gr. ion) flower (Gr. anthos). In their native Usambara Mountains cloudforests, the plants are threatened with extinction. 
Development and tourism
Today, the population of the Usambara Mountains region has one of the highest growth rates (about 4% compared to the Tanzanian national average of 2.1%), a staggering amount of poverty, and highest densities of people in all of Tanzania.  Most of the inhabitants are subsistence farmers who rely heavily on the forests around them for timber, medicinal plants, clearing for agriculture, and fuel wood. 
70% of the original forest cover of the West and East Usambaras has been lost.  Major land and forest degradation remain a pressing issue.
There are still many places that attract visitors looking for experiences beyond developed tourist resorts. These include the trade town of Lushoto (German colonial era Wilhelmsthal), the once popular German resort Amani Nature Reserve and farm, and the Mazumbai University Forest, which is considered the last example of a pristine tropical forest in the East Usambaras.
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- Forest Conservation in the East Usambara Mountains, Tanzania by A.C. Hamilton, R. Bensted-Smith and IUCN Tropical Forest Programme (1989, Illustrated book)
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|Wikimedia Commons has media related to Usambara Mountains.|
- UsambaraMountains.com: Usambara Mountains website
- Bird watching in the Usambara Mountains
- Tropical-biology.org: Introduction and fieldguide for the Amani Nature Reserve
- Kew.org: The Botanical Research Institute at Amani Nature Reserve