Moel Siabod (Foel) Slate Quarry and Slab Works is one of two slate quarries to the east of Moel-siabod on the Gwydir (Ancaster) Estate, which may have operated from the end of the eighteenth century, but was certainly being developed in 1838-40. The complex comprises a series of ruined buidlings and trackways, a large quarry (now flooded) and extensive slate spoil heaps. The quarry site has been recorded by participants of the summer Industrial Archaeology Course at Plas Tan y Bwlch, who recorded a series of `waliau?, three-sided shelters used by quarry men for splitting and dressing the slate. The quarry worked intermittently until 1884.
M. Railton, North Pennine Archaeology, 7th January 2011

Other sources include: A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.73.