Marston meets a man named Basilio Aguirre Olmos de la Vargas (Or Basilio for short) in Sidewinder Gulch, west of Tesoro Azul, and after a short talk, Basilio asks Marston if he can help him find a rock that he is looking for on a map he's holding. Then, he reveals that he wants to find the hidden treasure of his family, dating back to his Aztec roots. He asks Marston if he can help him find the other locations where the three other pieces of his map which combined, will lead him to his treasure, which Marston accepts.
Before this Stranger will appear on the world map, the player must complete:
After speaking with Basilio Aguirre Olmos de la Vargas, the player must:
- Find the first piece of Basilio's treasure map in Sidewinder Gulch.
- Find the second piece of Basilio's treasure map near Primera Quebrada.
- Find the third piece of Basilio's treasure map near Alta Cabeza.
- Ride to El Matadero and give the map to Basilio.
- Follow Basilio into some nearby caves to look for the treasure.
This stranger mission requires the player to find pieces of Basilio's map so he may find his ancestor's treasure. Without the map, the treasure cannot be found.
- The first piece is on a cliffside in Sidewinder Gulch just after meeting with him. Look for an unusual stone pile identical to the ones needed to find for the completion Treasure Hunter challenges.
- The second piece of the map is located inside a broken down house in Primera Quebrada (south-east area of Mexico).
- The third piece can be found at Alta Cabeza (just south west of El Matadero) near the north-east side of the hill.
After collecting the pieces, head over to El Matadero and talk with Basilio. After the player gives him his map he will rush off in excitement into the caves east of town and have to be met up with in there. At this point, Basilio will be searching the floor for an opening. Once Marston finds it, Basilio will cheer in happiness and lift open the stone hatch. Unfortunately, there was no treasure at all. Basilio is shocked and runs out dismayed and defeated, leaving Marston inside the caves.
- At the second map location near Primera Quebrada, there is a graffiti on a stone wall. The graffiti reads "I DON'T UNDERSTAND IMNFINITY", which is a cheat code to grant an infinite Dead-Eye meter.
- Oddly enough, if one starts the quest as John, and finishes as John, Basilio will say "10 years of my life wasted!" However, if you finish with Jack, he says the same thing, as if no time had passed at all.
- If starting the quest in 1911 then finishing it in 1914, he humorously comments saying that you looked younger; this may only happen when wearing Marston's old clothes.
- After completing the quest, Basilio can sometimes be found back outside at El Matadero, where the player originally came across him before heading into the caves.
- Basilio's last name is Aguirre. This may be a reference to the 1972 film ('Wrath of God') by Werner Herzog. In the film, a character named Aguirre is driven insane in search of El Dorado, the mythical city of gold.
- If for some reason the player does not see this Side-mission appearing on his map, he will have to venture out to Sidewinder Gulch for it to properly appear.
- The treasure is actually the mask that belongs to Ayauhtéotl (from the Undead Nightmare DLC), because the tunnel under Escalera (leading to the mask) matches the map.
- This is the Stranger Side-mission that most players tend to miss since it is started in a fairly remote area of the map that is not commonly traveled.
- After Basilio finds out the treasure doesn't exist and the mission is completed, John may say, "Well that about sums up my luck recently," just like when he loots dead bodies.
- If you kill Basilo right after he gives you the map and gets on his horse, he may have almost 50 rounds of pistol ammo on him.
- [platforms tag needed] When starting the mission, if you leave Sidewinder Gulch without getting the next piece of the map, the stranger mission advances (reason unknown).[verification needed]
Complete a task for a Stranger.
Complete 15 tasks for Strangers.
Attain 100% List in the singleplayer game completion list.