Mines in western Zacatecas, Mexico had their greatest development from 350 A.D. to c. 700 A.D. by colonists from classic Teotihuacan. The article describes the shafts, tunnels and rooms. They were dug in gravel beds covered by an unbroken caliche top. The tunnels had occasional retaining walls of blocks. The tunnels and rooms were dug with the principle of arched support clearly in mind. When rooms became enlarged, pillars of the mineral-bearing strata were left to provide roof support. Splints for lighting, stone scrapers, mauls and axes were found in the mines. -- AATA