[1] Slate was initially taken to a wharf on the River Dwyryd for onward transport, but in the 1860s, three inclines were built to link the quarry to the road at Tan y Manod.

The quarry was known for the use of ceir gwyllt (wild cars), simple devices that allowed the quarrymen to ride down the inclines to the Tan y Manod road at the end of the day.

From the quarry, a track passed around Mynydd Manod and led down to the River Dwyryd at Maentwrog, enabling slates to be exported to market by boat.

[9] The connection to the Ffestiniog and Blaenau Railway appears to have been made in late 1869, as around 300 yards (270 m) of the fourth incline remained to be completed in July 1869.

The third and second inclines were 1,326 yards (1,212 m) long, with a very short connecting track between them, and at the upper end was the Graig Ddu slate works.

[8] The first three inclines were renowned for the quarrymen's use of ceir gwyllt (wild cars), a device akin to a skateboard which sat on one rail, with a double flanged wheel at the front and a V-shaped notch at the back.

In an attempt to reduce accidents, a captain was the first to descend, with the others following, and it was his job to ensure that progress was steady and orderly, although this did not always stop abuses of the system.

[12] These devices were only used at Graig ddu because the exit incline from the mill level was both very long and of a relatively shallow pitch, running across the face of the hillside to the east of Tanymanod, rather than directly up and down.

However, some did not bother, and the Oakeley surgeon cited the case of a man from Graig Ddu whose hand had been crushed and required amputating.

On arrival at the hospital, he had not been admitted, because the quarry agent would not guarantee that the costs of the operation would be met, although he was later treated elsewhere by the surgeon.

[5] Graig Ddu was one of the early sites to use compressed air drills and winches, derived from steam-powered compressors.

In 1925 a gas engine was installed to provide a more reliable source of power for the mills, and at some point a hydro-electric plant was built part way down the second incline.

While a small number of the quarrymen lived in barracks at the top of the site during the week, most did not,[19] and the use of wild cars to descend from the quarry at the end of the day continued until 1939.

The quarry was then owned by the Alfred MacAlpine group, who invested in earth moving machinery and in modern sawing and dressing tables.

[22] The planning permission under which the quarry was reopened covered extraction up to 31 December 2022, and allows them to produce 15,000 tonnes of product each year.

However, by the end of 2022, there will still be large reserves of rock at the site, and Welsh Slate have applied to Gwynedd Council to extend the operation until 2048.