Pwllclai Mine worked the Pen-yr-hwylfa Vein, which extended in a north-easterly direction from Pen-yr-hwylfa Farm at SJ 1890 7370 toward Milwr. Shafts and spoil mounds scattered around Pen-yr-hwylfa Farm, Pwllclai, The Crooked Horn public house, and a house known as The Mount, which is situated adjacent to the A55. Large shafts remain at several locations, including SJ 1875 7380, SJ 1850 7380, SJ 1850 7355, SJ 1855 7375, SJ 1905 7405, SJ 1910 7405, SJ 1905 7365, and SJ 1905 7360.