Between 1826 and 1828 the Rothschild's Royal Cambrian Company attempted to locate commercially viable slate deposits on land belonging to the Crown, on the eastern slopes of Moelwyn Bach.

[1] Considerable effort was expended, as Nathan Meyer Rothschild employed John Rogers from Wrexham to construct a cart road, which wound its way up the side of the valley to reach the quarry.

Attention then switched to the southern flanks of Moelwyn Mawr, where a lawyer from Ruthin called Humprhey Jones had opened a quarry by 1841, but activity at the site was very intermittent.

[1] The next major advance was in 1860, when the Great Moelwyn Slate Company Ltd. was founded and paid £9,890 to buy the quarry from Thomas Cooper Smith.

[1] Chambers were excavated underground, but as there was no reliable source of water to provide power, the mill was built at some distance from the workings, and at a lower level, so that a 40-by-4-foot (12.2 by 1.2 m) waterwheel could be fed from Llyn Stwlan.

Three barrack buildings were erected, and whereas at most quarries, these were provided for the workers, at Moelwyn they were occupied by whole families, who lived there, rather than lodged there during the working week.

James Wright, also from London, was employed as engineer, and by 1866, the transport of slates by pack horse had been superseded by a spectacular series of seven inclines to descend some 1,100 feet (340 m) to reach the Ffestiniog Railway close to the northern end of the Moelwyn Tunnel.

[7] Large scale Ordnance Survey maps of the area were published in 1889 and 1901, but both correspond to periods when the quarry was not in production, and so although the formation of the main tramway and inclines can be seen, and the location of the mill and its water wheel is evident, few other details can be gleaned from this source.

Finished slates were initially transported to the Ffestiniog Railway at Penrhyndeudraeth by pack animals, using Moelwyn's traditional route, but subsequently, two inclines were built to connect to the Croesor Tramway.