Green’s Dictionary of Slang

(US) a euph. version of god-damn adv.

1892		Century Mag. (N.Y.) June 263/2: Law suits, Mr. Huntley, is gold darn uncertain [DA].
1894		J. Frye Fables of Field and Staff 97: ’Twas gol-dum cold out ther’.
c.1935		‘Betty Co-Ed’ [comic strip] in B. Adelman Tijuana Bibles (1997) 58: This is gol-darn swell of you gals.
1943		in A.J. Liebling Honest Rainmaker (1991) 76: It’s surprising how quick come to life when that Paddock Bugle gol darn doth blow.
1999		Pittsburgh Post-Gazette 9 June 🌐 If cheating makes you so goldarned wretched, how come Kuralt always seemed so jolly and wise?
2001		T. Hayward Playing With Fire 24: I thought you sounded sexy on the phone, but I wasn’t expectin’ you to be so goldarned pretty.