Pen-y-ffridd slate quarry is located on the west side of the Conwy valley, in forestry to the south of Llanrhychwyn. It comprises a line of workings - mostly open with some underground - extending over about 450m along a rocky escarpment. Here, the slate outcrops on a hill-slope under a dolerite sill. Eventually there came a time very early on when no more could be won from the open workings and so a series of entrances had to be made, each one leading to a chamber or two. The site preserves the early system whereby the roof is supported on pillars of slate that are left unquarried. It operated from the late eighteenth century until 1865, with finished product carted to the quay at Trefriw via Llanrhychwyn.

Sources:
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), pp.59 & 130.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.77.

David Leighton, RCAHMW, 25 February 2015