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of Dinas, near Carnarvon
1872 The North Wales Narrow Gauge Railways (Moel Tryfan Undertaking, to give it its full name) was a 1 ft 11½ in (597 mm) gauge railway running from Dinas to Bryngwyn, Wales, which was authorised by Act of Parliament. The same act authorised a branch from Tryfan Junction to South Snowdon. Subsequently the railway chose to regard the line from Tryfan Junction to Bryngwyn as the branch. 
1876 The North Wales Narrow Gauge Railways (General Undertaking) from Porthmadog to Beddgelert and Betws-y-Coed was officially abandoned. The line from Porthmadog to Beddgelert eventually completed by the Welsh Highland Railway was the later Portmadoc, Beddgelert and South Snowdon Railway.
1877 Opened from Dinas to Tryfan Junction and Bryngwyn.
1878 Opened to Snowdon Ranger.
1881 Opened to South Snowdon (Rhyd Ddu).
1885 The Carnarvon and Bryngwyn extensions were authorised, but these have not been proceeded with. 
1916 Closed to passenger traffic. Goods service continued running on an "as required" basis until about 1922 when the railway became part of the Welsh Highland Railway (additional Welsh Highland trackage from Rhyd Ddu to Porthmadog opened in 1923).
There are two locations which have been called South Snowdon. One is Rhyd Ddu and the other is the South Snowdon Quarry in the Nant Gwynant Pass and this was the original intended destination of the Portmadoc Beddgelert and South Snowdon Railway. That company later applied for and received a light railway order to build from Beddgelert to Rhyd Ddu and commenced construction on that section.