To start the Treasure Hunter quests, find your first map at a camp site outside of McFarlane ranch. It will appear randomly inside a chest. After that, use the map and the descriptions below to find the treasure:

RANK - LOCATION
Rank 1 - ???
Rank 2 - go to Vente's Place near Lake Don Julio and easily make your way by the mountains to find this easy treasure.
Rank 3 - Head to The Scratching Post, the camp where you meet the soldiers that give you the army uniform. Up the mountains, easy.
Rank 4 - Head to Sepulcro graveyard in Mexico, just south of there are a pair of tress, head past them to reach another bunch, search the area.
Rank 5 - Head to Casa Madrugada in Mexico, follow the map along the mountains and if you climb on foot on a cliffy part you'll find your treasure.