Moel-y-Faen is a large quarry located on the northern slopes of Llantysilio Mountain, above the Horseshoe Pass. Quarrying here may have begun as early as the seventeenth century, but mainly developed following connection to the Llangollen (Ellesmere) Canal (NPRN 405725) by an extension of the Oernant tramway (408164) in 1857. This was the only canal within Wales that carried any significant amount of slate, at least on the first leg of its journey from the quarries. Slate was loaded onto it at Pentrefelin, one of five separate locations, brought down from both the Moel y Faen and Bwlch yr Oernant quarries (NPRN 420091).
They were mostly open workings with some underground operations, on land owned by the Wynnstay Estate. There were three main workings which deepened into pits with some intermediate hillside working. The quarry mainly produced roofing slates, output at 2380 tons in 1882 with 84 men. By 1898 only 28 men were employed. The quarry ceased working in the 1940s following some years of very limited working.
In the early 1990s the three main pits were still visible with extensive areas of tipping. Vestiges of buildings, including dressing sheds, weigh-houses etc, inclines and winding houses. Some underground chambering was also evident. However, since the late 1980s extensive reclamation of slate waste for use in civil engineering projects has taken place followed by landscaping. The present status of the archaeological remains is unknown.

Sources:
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), p.222.
Ordnance Survey County Series 25-inch maps: sheet Denbighshire XXVII.14, editions of 1875, 1899 & 1912.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.204-5.

David Leighton, RCAHMW, 19 February 2015