|Dates of operation||1862–1979|
|Track gauge||3 ft 6 in (1,067 mm); 2 ft (610 mm)|
Pen-yr-Orsedd Quarry was a slate quarry in the Nantlle Valley in North Wales. It was one of the last slate quarries operating in North Wales and the last operating on the Nantlle area, finally closing in 1979.
The Pen-yr-Orsedd quarry was one of the major slate producers of the Nantlle Valley, supplying over 10,000 tons of product in 1864. It was also the last quarry in the vale that commercially produced slate, closing in 1979.
In 1862 the quarry was connected to the Nantlle Railway, with 3 ft 6 in (1,067 mm) narrow gauge lines extended to all but the highest levels of the quarry. Most levels of the quarry had both 3 ft 6 in (1,067 mm) narrow gauge and 2 ft (610 mm) narrow gauge trackwork, many with mixed gauge tracks. The Nantlle Railway connection was used up until 1963, while the internal 2 ft lines continued in limited use until the end of quarrying.
|Baladeulyn||De Winton||0-4-0VB||Sold to Glynrhonwy Slate Quarry in 1895|
|Starstone||De Winton||0-4-0VB||Thought to be sold to Glynrhonwy Slate Quarry in 1894 where it was renamed Padarn.|
|Inverlochy||De Winton||0-4-0VB||1877||Possible ex-Pen-y-Bryn Quarry. Scrapped 1937|
|Glynllifon||De Winton||0-4-0VB||1880||Scrapped 1937|
|Rhymney||De Winton||0-4-0VB||1875||Scrapped 1933|
|Chaloner||De Winton||0-4-0VB||1877||Sold to a private collector 1960; now preserved at the Leighton Buzzard Light Railway.|
|Gelli||De Winton||0-4-0VB||1893||Withdrawn 1945, still intact at quarry 1952; believed scrapped|
|Pendyffryn||De Winton||0-4-0VB||1894||Sold 1965|
|Arthur||De Winton||0-4-0VB||1895||Scrapped 1956|
|Victoria||De Winton||0-4-0VB||1897||Scrapped 1956|
|Kelso||Vulcan Foundry||0-4-0VB||1893||Withdrawn 1945, still intact at quarry 1952; believed scrapped|
|Britomart||Hunslet||0-4-0ST||707||1899||Sold in 1965, now privately owned and running on the Ffestiniog Railway|
|Sybil||Hunslet||0-4-0ST||827||1903||Sold in 1965, now privately owned|
|Una||Hunslet||0-4-0ST||873||1905||Sold in 1963, now at the Welsh Slate Museum, Llanberis|
|Diana||Kerr Stuart||0-4-0T||1158||1917||ex-Oakley Slate Quarry, Blaenau Ffestiniog. Privately owned. Based on the Bala Lake Railway in Mid Wales|
|No. 1||Ruston & Hornsby||4wDM||235712||1945|
|No. 2||Ruston & Hornsby||4wDM||235711||1945|
|No. 3||Ruston & Hornsby||4wDM||226298||1943|
|No. 4||Ruston & Hornsby||4wDM||226264||1943|
|4wPM||Sold or scrapped|
- Boyd, James I.C. (1990). Narrow Gauge Railways in North Caernarvonshire, Volume 1: The West (2nd. ed.). The Oakwood Press. ISBN 0-85361-273-0.