Folsom Prison in California offers a great illustration of the dimensions of rock-labor in late 19th/early 20th century prisoners' lives. It's not quite the stereotypical Cool Hand Luke chain gang, of course, but its actual granite quarry provides for some...concrete...investigation.
Prisoners slaving in the Folsom quarry did produce regular granite blocks for building construction. The prison itself is, of course, one of the results of that. But it was also sold to the market.
During the late 19th and very early 20th centuries, yes, the quarry also produced crushed gravel, which is to say, some Folsom prisoners were forced to spend their days crushing rock, transporting crushed rock, etc. So while that's a stereotype of chain gang movies, it has a basis in reality. And in this case, the gravel was absolutely sold to the public. Primarily it would be used in road construction.
And the prison/the state made bank off prison labor. Well, at least initially. The 1929 Hawes-Cooper Act and the 1938 Ashurst-Sumners Act restricted to whom prisoners could sell crushed rock and other products (San Quentin's jute mill was a major moneymaker for California as well). After that, the state was the only legally permissible customer.
But that didn't mean Folsom stopped or even slowed down its quarry production. Brutal punishment and physical exhaustion were just as important motivators as the money.
At Folsom, assignment to the quarry was considered the absolute bottom, worst possible work. It was the default assignment for new prisoners, a return assignment for misbehavior, and much much harder to be 'promoted' out of if the prisoner was black. The full process included:
Indeed, 20th century prisoners at Folsom referred to quarry detail as "the Concentration Camp." But the prison did not, as it were, shoot a man in Reno just to watch him die--it also made a very large profit.
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