Gloydius strauchi
Habitat
High mountains, even above the tree line at over 4,000 m
Range
Western China (eastern Xizang and Qinghai east to Ningxia, southern Shaanxi and north-west Sichuan)
Size
Probably not much more than 50 cm; largest female 54.7 cm
Gloydius strauchi, the Tibetan or Strauch's pit viper, is a small venomous pit viper native to western China, from eastern Xizang and Qinghai east to Ningxia and southern Shaanxi, plus north-west Sichuan. It jointly holds the altitude record for pit vipers, being found above the tree line at over 4,000 m. (The Reptile Database; Wikipedia, general species account)
The largest male examined in one study was 51 cm and the largest female 54.7 cm. It has a pattern of four longitudinal stripes, clearly visible in young snakes, while older ones may be dark or uniformly black. It has 21 keeled dorsal scale rows at midbody, and the higher count separates it from Gloydius monticola. (Wikipedia, general species account)