Bryn Hafod-y-wern Slate Quarry in the Ogwen valley is located a short distance to the north-east of Llanllechid on the lower west slopes of Moel Wnion. A pit working, the lack of available land downhill meant that it could not be made self draining. All material had to be uphauled to the mill, and waste further uphauled to lengthy tipping runs. Also, the need to re-use a limited water supply (derived from Llyn Caseg) meant a less than ideal layout of the mill area.
The quarry is notable for various developments. In 1849 attempts were made here to devise rotary drills, a device which in 1852 was worked by a portable steam engine. In 1847, the directors of the quarry bought a 20 horse power engine from Tyrrell's of Dentford to work railed inclines, an attempt which failed and water wheels were used instead. But the quarry's reliance on water led it into dispute with Lord Penrhyn, the major local landowner, over the right to draw on nearby streams.
Although the site is relatively undisturbed (in 1991) buildings are ruinous and the pit filled with water. Incline formations and tramroad lay-outs are still clear. Traces of slate ways on which wagons were run point to financial constraints on the entrprise. The leat from the river Caseg (over several kilometres) to two reservoirs can be traced. An impressive feature is a row of slab pillars, many of them now leaning over drunkenly, which once carried wooden launders.

The quarry may have been worked as early as the seventeenth century. It was certainly in use in 1780 when it was operated by the Pennants but abandoned by them in 1845, probably because of excessive working costs. It was re-opened in the same year by the Royal Bangor Slate Company (who in due course built the mills) but closed in 1884 when the Pennants cut off the water supply.

Sources:
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), pp.67, 80, 140 & 142.
Lindsay, The History of the North Wales Slate Industry (1974), p.311-2
Ordnance Survey County Series 25-inch maps: Caernarvon XII.2, edns. 1889, 1900 & 1914.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.19-20.
RCAHMW Air Photos: AP94-CS 1060; AP945135/44

David Leighton & John Wiles, RCAHMW, 14 January 2015