When a city becomes devastated, a Devastation token is put upon it. Any Clues, Expedition Encounters, Mystic Ruins Encounter or defeated Investigators are discarded from the map or their decks. Clues that would be placed on the space are not placed if spawned, and the space no longer counts as a City space for purposes like Darrell Simmons's ability.
The player will no longer draw a Location Encounter when having an encounter there and may not draw a General Encounter. Instead, they will draw a Devastation Encounter. The investigator may still draw an Other World Encounter if a Gate is on the space.