Big Orange, n. — Green’s Dictionary of Slang

Big Orange n.

[on model of Big Apple n.; the ref. is to the state’s orange groves]

(US) Los Angeles, California.

1982		G. Sculatti Catalog of Cool 75: Los Angeles [...] a no-nonsense, non-snob appraisal of the Big Orange.
2002		Fables 🌐 Gene-Michael Higney was born in Brooklyn but is now an ex-New Yorker, transplanted (sort of like a potted fern) from the Big Apple to the Big Orange, Los Angeles.