This quest is not available in game.
Cairne Bloodhoof in Thunder Bluff wants you to bring him the Horn of Arra'chea.
You have passed the Rites of the Earthmother and earned your place in Thunder Bluff.
But in order to maintain the spot that you strived so hard to achieve, you must continue to prove your worth to your people.
We are hunters, <name>. Down below in Mulgore there is a mighty kodo named Arra'chea. Show me your skills in the ways of tracking and hunting by bringing me the Horn of Arra'chea.