Tanyrallt slate quarry is located on enclosed land less than one kilometre south of Talysarn. An open pit working, the quarry opened in 1805. Material was uphauled to the north and a mill later built on waste on the opposite side of the public road. It was worked intermittently. A tonnage of 1000 with 40 men, recorded in 1873, may have been an exceptional peak. Some very small scale working was done here up until the 1980s.
The quarry was connected to the Caernarvonshire SQR via Fron Heulog. It is stated to have had up to three waterwheels, one of which may have been for pumping. For a time the quarry operated with the small Twll Coed quarry nearby (at SH49165189).
The pit is now flooded and some sheds from later working remain (in 1991); also the uphaulage incline formation, traces of early buildings - including possible barracks - wheelpit and the abutments of the bridge over the road.

Sources:
Ordnance Survey County Series 25-inch maps: sheet Caernarvonshire XXI.9, edition of 1889.
RCAHMW air photos: 94-CS 0968; 945127/51.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), pp.56 & 57.

RCAHMW, 11 March 2015