The lowest point in the valley is 430 meters above sea level; the highest is the peak of Mount HsinWangLing, at 2,481 meters. The four main settlements upriver are Minzu (Nangisalu in the local aboriginal language), Minchuan (Mangchu) and Minsheng First and Second villages (Takanua).
There is plentiful wildlife: 29 mammal species, 97 bird species, 30 types of reptile, 16 amphibians, and 18 fishes. There are also 89 butterfly species.
On January 1, 2008, the township was renamed from Sanmin to Namasia, as the name of Sanmin (taken from the Sun Yat-sen's Three Principles of the People), was considered an overly political name. Rather, the name Namasia was chosen, as it is the name of a local river in the Tsou language, while its meaning is "better and better" in the Bunun language. The population of the township is majority Bunun with a substantial Tsou minority.