Slate production in Wales developed as an organised concern in the late 18th century. The industry's main period of growth and expansion occurred during the 1830's with significant development between 1831 to 1882 and rapid decline in the 20th century. The chief commercially significant slate producing areas in Wales were central Caernarfonshire, including Bethesda, Llanberis and Nantlle; the area in northern Merionethshire between Blaenau Ffestiniog and Capel Curig and adjacent parts of Caernarfonshire; the Corris area in southern Merionethshire and adjacent parts of Montgomeryshire; the area between Llangollen and Corwen in Denbighshire and eastern Merionethshire; the Preselau area of Pembrokeshire and adjacent parts of Carmarthenshire.
Croesor Quarry, at Moelwyn Mawr, to the north of Merionethshire was an underground operation dating from 1846. James Wyatt, who had formerly been Lord Penrhyn's agent, was director of the Croesor Quarry until 1866. In 1862, its annual output was 74 tons rising to 1,190 tons in 1864. From 1866 to 1874 the Croesor United Slate Company operated it. In 1867 it employed 175 men, by June 1868 the number was reduced to 111.
In 1875 the Croesor New Slate Company Ltd acquired the business, but by 1882 they had given up the quarry. In 1895 the Park and Croesor Quarries were amalgamated to form the Park and Croesor Slate Quarries Company Ltd, with a head office at Penrhyndeudraeth near Porthmadog. Annual output was low and a receiver was appointed in 1914. The quarries finally closed in 1930.