forty-niner, n. — Green’s Dictionary of Slang

forty-niner n.

[the image is of cocaine as gold dust n. (1) due to the Californian Gold Rush of 1849]

1. one who is looking for a rich wife.

1922

Morn. Tulsa Dly World (OK) 7 May 29/7: Forty-niner - Man who is prospecting for a rich wife.

2. (US drugs) a cocaine user.

1959		J.E. Schmidt Narcotics Lingo and Lore.
1975		Hardy & Cull Drug Lang. and Lore.