Green’s Dictionary of Slang

(US) a generic nickname for anywhere considered far away.

1935		‘Miscellany’ AS X 80/1: With its hills, hollows, and swamps, southeast Missouri is well adapted to propagation of the Podunk idea. . . Emerging from Nigger-Wood Swamp, one is likely to find himself in the vicinity of Gobbler’s Knob.
1968–69		in DARE.