Complete 'A Fisher of Fish' stranger mission:
Complete at least one set of cigarette cards, He will offer to sell you the map for $10 if you accept and $5 if you decline. Find at least one buried treasure (there are many maps leading to the treasure, you can purchase the first map from Maximo you can meet him in Chapter II near Flatneck Station. Find 9 graves of your fallen gang members (see Paying Respects trophy), Make a sketch of at least one point of interest, Capture 6 gang hideouts (you should do it during the main story line), Encounter one gang ambush (you will experience it even more than once), a man bitten by a snake, random shootouts, some fella lost in the forest, woman whose horse died etc.), they are completely random so you have to travel a lot,
Finish 5 bounty hunter missions (you can start them by visiting sheriff's office in Valentine), Finish at least 10 stranger missions (question marks on your map), Finish the main story line ( 107 missions), You can follow your progress on Rockstar Games Social Club !