Search Franklin's bookshelves to find a book titled "Red Dead", authored by J. Marston. In Red Dead Redemption, Jack Marston mentioned that he was going to write a book about his father and the Wild West.
There are two locations in Grand Theft Auto V called "Cholla Springs Ave" and "Armadillo Ave" that can be found in the rural area of the map. This is a reference to Red Dead Redemption's Armadillo Town and the surrounding region of Cholla Springs.
There is a farm south of the prison that looks exactly like John Marston's farm in Red Dead Redemption.