It is obvious now, the interconnectedness of all things. It lies in plain sight, in our most treasured texts, in our forgotten temples, in etchings on cavern walls. All that remains now is to connect the dots.
During step 7 of setup ("Separate and Place Decks"), shuffle all Expedition Encounter cards together regardless of card back and split them into two decks.
Place an Active Expedition token on each space that corresponds to the illustration on the back of the top card of an Expedition Encounter deck. If the top card of either Expedition Encounter deck changes for any reason, move the Active Expedition tokens to the appropriate spaces.
During the Encounter Phase, an investigator on a space containing an Active Expedition token may encounter it by drawing and resolving the top card of the corresponding Expedition Encounter deck.
Any effect that refers to the Expedition Encounter deck affects both decks. Any effect that refers to the Active Expedition space affects both spaces that contain an Active Expedition token.