Piedras Negras is located in Saltillo city, Mexico at the 28.7001, -100.5235 coordinates. Distance from Piedras Negras to other cities. are listed below, click on the city name to find distance between. Distance from Piedras Negras to Torreon 453 km, to Monclova 218 km, to Ciudad Acuna 81 km. The green marker indicates the location of Piedras Negras.