Deeside Slab Quarry is an open working located high on the southern slopes above Nant y Pandy, a tributary of the Dee near Glyndyfrdwy. The quarry may have developed as early as the 1940s. This was an open hillside working with a substantial water-powered mill complex at Nant-y-pandy (NPRNs 309750-1), about 2 km to the north-east along a tramroad which connected the two, wooden rails at 2ft 6" gauge covered with iron sheets. In the 1870s this was extended, in steel, to the Moel Fferna quarry (308669), a short distance to the south-west. The tramroad continued via a table incline Glyndyfrdwy station. Here there was a massive wooden gantry to facilitate trans-shipment of slab.
In 1898, 38 men were employed. The quarry closed in the 1920s though the tramroad continued to serve Moel Fferna until the 1930s; one of the last such railways to be laid down and probably the last to close. Very little now survives at the quarry site aside from the vestiges of small buildings. The tramroad formation is still largely intact; some wooden rail was still visible in the early 1990s though the iron sheathing had been removed.

Sources:
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), p.234 & Fig.227.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.202.
Ordnance Survey County series 25-inch maps: sheet Denbighshire XXXVIII.4, editions of 1875 & 1900.
RCAHMW air photos: AP 955026/50-51.

David Leighton, RCAHMW, 29 January 2015