To start, you will need to track down all the famous fighters in the Arrow mission. After the beginning of this stage of the game, Arthur needs to find Flaco Hernandez, kill him, and after that the first treasure map seems to be in his hands.
Map 1
After receiving the first map, Arthur will need to go to a place located South of Lemony and West of Ringneck Creek. The search target will be a hollow tree inside. It contains the second map of the quest.
Map 2
As soon as the second map was in Arthur's possession, he would have to walk to the steep hill that lay to the West of the Trading post in Van Horn. There will be a small pile of stones. The third card is hidden under it.
Map 3
The starting point of the treasure hunt will also be the Trading post in Van Horn. To the Northwest of it is the Elysian pool. On the North Bank there is a waterfall that hides the secret entrance to the cave.
Here you will have to put a lot of effort to achieve the goal. A flashlight will help Arthur. With its help, he will need to find the first ledge and walk along it. Unfortunately, the fall is inevitable, but immediately after it, you can find a path that goes down to the right.
At the end of this path is the entrance to the tunnel. It has fairly low ceilings, and in order for Morgan to pass it, you will need to sit down. Once Arthur is able to stand up to his full height, he will need to turn left, lean over the ledge and find the next ledge. After examining a large boulder, Arthur will find four gold bars.