The Penyrorsedd slate quarry, close to the village of Talysarn, Llanllyfni, Caernarfonshire, was first developed in 1816. When it was worked by William Turner. Penyrorsedd was owned and managed by Mr. Kane and his sister from 1820 until 1854.
In 1862 the quarry was connected to the Nantlle Railway, with 3 ft 6 in (1,067 mm) gauge lines extended to all but the highest levels of the quarry.
In 1863 it was bought by W A Darbishire and Co, after which it underwent substantial modernisation, reflecting the use of both water and steam power. The Darbishire family expanded the operation with three mills built in 1860, 1870 and 1898. In 1882 the Penyrorsedd Slate Quarry Co. employed 230 men. In the late 19th century, the quarry was worked by 450 men and despite the decline in the slate industry, by 1937 there were still 351 workers employed at the site. William Arthur took over the Penyrorsedd Slate Quarry at Nantle over a long and prosperous period.
The quarry closed in the late 1970s Reopened and finally closed in 1997.
Nantlle Valley Quarries