Blaen-y-cwm Quarry is located on the east side of Manod Mawr, to the east of Blaenau Ffestiniog. It comprised three distinct workings, both pit and underground, the earliest dating from the 1820s. Much developed during the 1870s when the mill was built (possibly water powered with steam back-up), and the powered connection to the Rhiwbach Tramroad made. The quarry is unusual in lying below its exit railway. The underground workings lower down the site to the east appear not to have been successful.
Prior to the use of the tramroad via Blaenau Ffestiniog, material was carried via Cwm Machno to Trefriw. The quarry closed in about 1914.
Remains are extensive. Main surviving features (1991) include the mill, engine house and coal store, mill waste chutes, and several buildings including a barracks of four separate units each of two rooms. There is a also a lavatory block built over a large pit - the wheel pit of an earlier mill - and a small reservoir dug behind the Rhiwbach Tramroad formation.

Sources:
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.124.
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), 143 & 151.

David Leighton, RCAHMW, 12 January 2015