Evergreen was a town close to South Park. Its inhabitants were driven mad by overpopulation of homeless people. They finally decided to send their problem to South Park in the episode "Night of the Living Homeless", commercializing South Park as an ideal place for homeless people.
The entire city looks like it was devastated by a riot and civil war and the only remaining citizens are completely mad. Most of the population fled the town or were killed by other insane citizens.