Llwyngwern was a small quarry that only briefly produced more than 2000 tons of finished slate per year.

It worked a minor outcropping of slate away from the main veins quarried to the north around Corris and Aberllefenni.

[4] In 1853 it was re-opened by W.R. Williams of Dolgellau and was described as a well-developed quarry with a 30 feet (9.1 m) waterwheel powering the mill.

[1] By 1887, the quarry had dammed the local stream to form a header reservoir for the various waterwheels on the site, including one for the main mill.

The quarry was in the form of a deep open pit, accessed by a tunnel at the mill level.

A row of workers' cottages had been built beside the Afon Dulas and a gunpowder magazine was located north-west of the mill.

[6] In 1893, a new company Maglona Quarries Ltd. took over Llwyngwern,[7] (Maglona was commonly believed to be the name of a Roman fort on Sarn Helen at what is now Machynlleth[8]) In March 1895, quarryman Robert Ellis Jones was killed at the quarry when the rock face he was working on collapsed.

The incline was a water balance that used large tanks to counter-balance the weight of the ascending wagons.

Many of the men who lost their jobs left to find work in the coal mines of South Wales.

[15] In 1906 there was another fatal accident, when 19-year-old Henry Rees who had been working in the mill fell while walking through the tunnel to the main pit.

In 1906, an aerial ropeway was installed to lift waste rock from the bottom of the exit incline up the mountainside to a site south-west of the quarry reservoir.