The Tribe of the Two Rivers was a native American tribe that sheltered the Angel Metatron since his departure from Heaven. The tribe was the last tribe to hold its ground from European settlers and conquerors. They are known by the sigil which represents the Messenger of God, which pertains to Metatron. In exchange for giving the angel numerous books and other stories by humans, the members of the tribe were blessed by Metatron with immortality.
Sam recognises their sigil, which he read about during his time at Stanford. Dean investigates the local Native American museum, observing that the Two Rivers’ tribe leader asked of the people an offering of “stories”, while Sam awakens and woozily explores the hotel hallways, seeing the desk clerk deliver packages filled with books to a nearby room.