Goldthorn requires a herbalism skill of 150 to gather and usually found on top of small hills. On the route to farm Goldthorn, other herbs such a Fadelead and Liferoot can be found as they may spawn on the same maps. Goldthorn can be found at Alterac Mountains, Arathi Highlands. However Arathi Highlands is the best place to farm Goldthorn in WoW.
See below for maps of where to farm Goldthron in WoW.