Hafod y Llan slate quarry is located at the head of Cwm Llan, a tributary valley of the Afon Glaslyn, on the southern slopes of Snowdon. It was an open working believed to have been started in the 1840s, but possibly earlier in the nineteenth century.
The quarry was developed by Alan Searell who was from Devon and had various mining and quarrying interests in North Wales. The main period of development was from the 1860s to the 1870s when a tramway was built down the Gwynant valley. The water-powered mill was extended and converted to turbine operation (in 1869). A system of tramways and inclines brought material to the mill, finished product sent by a short tramway to the Cwm y Llan cart road which served the local copper mines. During expansion this route was superceded by a tramway down to Pont Bethania. From there, material was carted to the Croesor Tramway for carriage to Porthmadog. The quarry closed during the 1880s.
Surviving remains include (in 1991) workings on several levels, inclines, ruined buildings, and tramroad formations.

Sources:
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), pp.26, 122 & 190.
David Gwyn & Merfyn Williams (1996) `A Guide to the Industrial Archaeology of North West Wales?. Association for Industrial Archaeology.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.115-6.

David Leighton & Claire Parry, RCAHMW, 11 February 2015