Stonespire tribe refers to a tribe of tauren that lived in the Barrens. Most were wiped by the forces at Bael'dun Keep. Aside from a few survivors, they were wiped out by the forces of Bael'dun led by Prospector Khazgorm, and General Twinbraid who were searching their home for artifacts without concern for the local inhabitants.
While Gann Stonespire is member of a lost tribe, technically there is no reference that it is called the Stonespire tribe. However, most other tauren last names refer to tribe, Elder Stonespire is seen with the other tribal leaders such as Elder Bloodhoof and the NPCs with the Stonespire name tend to have specific skin tones, specifically grey and brown fur.