Slate quarrying began at Wrysgan in the 1830s, and was developed substantially in the 1850s. The workings were underground in a series of chambers in the Back and Old Veins of the Ffestiniog Series, exploited at five different levels which were accessed by adits from the from the surface. A small mill dating from c1850 (at SH6767845431) was replaced in 1865 by a larger water-powered mill at the given location, on the middle of the five working levels. The site suffered from water shortages, with a very small reservoir (LLyn Wrysgan, SH6764745336) supplied by a leat along the steep hillside; and in 1920 electrical power was introduced. The quary worked intermittently until the late 1940s.
At first the products were lowered down an incline into Cwm Orthin, where there was a loading platform whence slates were carried by pack animals. Access to the quarry for the men was by a zig-zag track and steps up this slope. In 1850 a new incline was built to connect with the Ffestiniog Railway some 625ft (190 metres) below.
W J Crompton, RCAHMW, 21 December 2011.