Gaewern Slate Quarry is depicted on the Ordnance Survey County Series second edition 25-inch map of 1901. The quarry was amalgamated with Braichgoch Slate Quarry (NPRN 40585) and Abercorris Slate Quarry (96191).
Workings at Gaewern were underground with some open working, established in about 1820. The quarry developed considerably after its connection to the Upper Corris Tramway by an incline passing under the main road. By 1873 200 men were employed. In 1884 it merged with Braichgoch and later a surface tramway connection enabled the latter's mills to be used. Wrought-iron fishbelly T-section rail was found to have been in use here, rarely found in internal systems.
Bulk working and road improvements have left little to be seen. However, in the early 1990s there was a well-preserved drumhouse, some building ruins and a reservoir at the top of the site.
Sources:
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), p.134.
OS County Series 25-inch map, sheet Merionethshire XLII.8, edition of 1901.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.184-5.

David Leighton & Claire Parry, RCAHMW, 4 February 2015