The story
Originally used in the phrase there’s gold in them thar hills, possibly a misquote of the phrase there’s millions in it (viz. the North Georgia mountains) uttered in Mark Twain's novel The American Claimant (1892) by Colonel Mulberry Sellers, a character thought to be based on Dahlonega Mint assayer M. F. Stephenson.
Etymology from Wiktionary, CC BY-SA 4.0.