The Pen-yr-Orsedd Quarry tramways were the industrial narrow gauge railways serving the Pen-yr-Orsedd slate quarry and connecting them to the Nantlle Railway. Pen-yr-orsedd was one of the last slate quarries in north Wales to use narrow gauge internal tramways, 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.