1862 ‘M. Twain’ 8 Feb. (1920) 51 We'll have a mill-site, water power, and pay-rock, all handy.
2000 M. Wright ii. 63 You had little chance of striking..‘pay rock,’ ‘pay shoot,’ ‘pay streak,’ or ‘pay vein’—dirt, earth, or gravel bearing heavy quantities of minerals, especially gold.