11. The explosions caused severe damage to the underground workings . 12. Ore was extracted from underground workings until 1915, when a small open pit was dug. 13. There are about 20 miles of underground workings . 14. The hill is " honeycombed " with underground workings , reaching from the summit to depths of. 15. Complex arrangements were written into the leases to ensure that the underground workings did not conflict. 16. The land above the underground workings , together with the surface quarries, became a National Nature Reserve. 17. Between 1975 and 2000 the lease to the underground workings at Dolaucothi was held by Cardiff University. 18. The underground workings were deepened and the crown corporation sought out additional deposits of uranium across Canada. 19. Idarado kept the underground workings and mill operations open at Telluride s Pandora hard-rock mine until 1978. 20. Just after 8 : 00 am an explosion occurred in the west side of the underground workings .
