The Collaborative International Dictionary
Pay rock
Pay dirt \Pay dirt\, Pay rock \Pay rock\, etc.
(Mining) Earth, rock, etc., which yields a profit to the miner. [Western U. S.]
a discovery, especially after an exploratory process, which yields a profit or sought-after benefit; -- used especially in the phrase ``to hit pay dirt''.
Usage examples of "pay rock".
The romance of a new mining-camp near the very peak of the Sierra Nevada addrest the sympathies of the young adventurer more than the hard work of prospecting for pay rock.