From ErfWiki

Proposed Canon

First Appearance: IPTSF Text 50

Efbaum is a Level 5 Haffaton City. It lies at the end of a yellow road and is Emerald in hue. It was once the Capital of the most powerful Side in Erfworld. It is the location of the Olive Garden where Judy Gale, the Overlord of Haffaton, is kept imprisoned.

Speculation

Efbaum may once have been Charlie's Capital.

Judy Gale refers to it as 'old el-Efbaum,' which may suggest that the city has been renamed, or that Efbaum is a nickname.

Real-World References

The City is, of course, related to the Emerald City from the Wizard of Oz and presumably named for the author of that story L. Frank Baum.

Its name may sound like 'F-Bomb' when spoken aloud.