Rhosydd Quarry is a slate mine northeast of Porthmadog in North Wales. Small-scale working of the site began in the 1830s, but was hampered by the remote location, and the lack of a transport system to carry the slates to markets.

They kept it running until 1930, but failed to find markets for the finished product. It was mothballed until 1947, when it was sold, but new plans to reopen it failed, and the pumps were turned off in 1948, after scrapmen had removed much of the machinery