11. Coal was extracted by room and pillar working in the Black and White mine and longwall mining in the Trencherbone. 12. Mine voids in the inclined slope resulted from the practice of room and pillar mining during the early 20th century. 13. The mines are located in Lea and Eddy counties, New Mexico, and are operated by the room and pillar method. 14. It was constructed using the room and pillar technique, where pillars of dolostone have been left to support the overlying rock. 15. Pink areas were a room and pillar mine at the time of the disaster, while retreat mining had been completed in the brown areas. 16. Stone was extracted by the " room and pillar " method, by which chambers were mined, leaving pillars of stone to support the roof. 17. Room and pillar mines are developed on a grid basis except where geological features such as faults require the regular pattern to be modified.18. Much of the city, particularly the northern portion, has been undermined by room and pillar extraction of coal that took place in the 1800s. 19. It has a grid of high, wide tunnels separated by square limestone pillars created by the room and pillar method of hard rock mining. 20. Quarrying is done using the room and pillar method, mining only half of the salt and leaving the remaining half to support what is above. 