The Mount Halkyn and West Halkyn Mines operated at the eastern end of the California Vein, which extends east to west across the Carboniferous Limestone of Halkyn Mountain. Mining activity in this area was extensive, with workings appearing to stretch eastward toward the wireless station from a reservoir near Pant-y-ffrith (SJ 2040 6955). The landscape is marked by numerous shafts and spoil heaps, with earthworks covering a significant area. The primary zone of activity seems to center around a large concrete-capped shaft at SJ 2035 6995, which features a stone wall revetment on its southern side, possibly indicating the remains of a former building structure.

Drained by Sea Level Tunnel.

In 1928, the Halkyn District United Mines took over operations of the sett, introducing modern infrastructure to support extraction and transport. An underground diesel railway system, installed by the company, was used to serve the workings of the mine.