Green’s Dictionary of Slang

1. craggy, physically tough.

1912		J. London Smoke Bellew (1926) 197: The speaker, a loose-jointed, hard-rock man from Colorado.
1926		(con. 1918) L. Nason Chevrons 176: I’ve been a hardrock man all my life.
1948		J.M. Cain Moth (1950) 216: He was like most other hard-rock men, shy on the inside as a young girl.
1961		H. Ellison Rockabilly (1963) 161: No longer the hotshot, hard-rock flak man who could sell sandboxes to Arabs.
1977		E. Bunker Animal Factory 84: Why else would a hardrock con put himself out on a limb for a pretty kid?
1990		S. Morgan Homeboy 123: He [...] was indelibly marked as a hardrock career convict by more tatoos than Joe had ever seen.
1998		Source Nov. 188: Doing what all the other hard-rock kids did.

2. (US) committed, full-time.

1971

R.D. Pharr S.R.O. (1998) 71: J&J were not by any means hardrock hustlers or vultures.