This is the most stark and least-visited of the major slate quarrying areas of North Wales, yet in many ways it is the most compelling. It is a multi-period valley-landscape, which sweeps from the foothills of the Snowdon massif to the Arfon plain and to the sea.
Slate quarrying is known to have been underway in the Roman period, and where outcrops of rough rock are still visible on the valley slopes at Ochr y Cilgwyn. Because the valley was owned by different estates, the slate veins were worked in separate quarries.
Here and there, pre-industrial farm buildings survive on the spaces between them, illustrating the change-over from an agricultural to a quarrying economy. This transition was only ever partial; many Nantlle quarrymen and their families retained a connection with the land by living on small-holdings, of which examples survive at Ochr y Cilgwyn.
Typically, the quarries were deep pits opened up on the slopes or the floor of the valley. For this reason, ambitious pumping systems had to be introduced. The sites of the waterwheels and flatrods at Penybryn quarry contrast with the surviving beam-engine of 1904-1906 at the nearby Dorothea quarry, the last Cornish engine installed from new anywhere in the world. Other instances of technology transfer to the valley are the Scottish ropeway ’blondin’ systems, of which examples survive at Penyrorsedd quarry, with their early electric motors, and at Blaen y Cae, associated with a steam winding engine. Substantial mill buildings survive in ruin and the route of the quarries’ main transport system, the Nantlle Railway and its tributary inclined planes, survive as linear features through the quarry landscape. Though it initially provided access to the slate quay at Caernarfon, it was cut back to a short length through the quarries in the period 1869-1872, which continued to operate with horse traction practically until its closure in 1963.
Quarrymen and their families have made a living in a difficult environment in the Nantlle valley, with little help or encouragement from landowners or investors. The most distinctive sites in this quarry landscape are the tip contractors’ workings, many of which date from the Great Depression, tiny shelters on the heaps of slate waste where unemployed quarrymen made roofing slates from rock that had been tipped in the good years.