Check this out: it’s a series of pics of the former Los Angeles zoo, which shut down in 1965. There’s another series of pics here. Update: The first link is no more. Second link still works.
Now you may be asking yourself: why did the zoo move and abandon these structures? Well, check out the pic there. See that? It’s a grill. Yup. It doesn’t take a rocket scientist to figure out that the animals were cooking and eating the weakest among them. All it took was a few families complaining that little Timmy saw a gazelle barbeque taking place out in the open and bang, the place was closed down.