Green’s Dictionary of Slang

(Aus.) the city of Charters Towers, Qld.

2003		Aus. Word Map 🌐 Charlie's Trousers The city of Charters Towers in northern Qld - an affectionate name used by those in the north, particularly school children. [...] Charlie's Trousers may be also a form of rhyming slang.
2020		Twitter 13 Feb. 🌐 — I think (guess) our flight made this detour because of the fires north of Charlie’s Trousers/inland from Ingham. — Charlie’s trousers? — Charters Towers = Charlie’s Trousers.