Mining at Onllwyn started in 1841, and there were many mines, large and small, around the valley. The coal washery at Onllwyn in the upper Dulais Valley is the modern face of coal production in south Wales. Operated by Celtic Energy, it is a processing and distribution hub for three large opencast workings in the vicinity. The main customers for the coal produced here are the power station at Aberthaw and the Corus steel works at Port Talbot.