Oakeley was located on the north side of Allt-fawr. On the south side lay Cwmorthin quarry had by the 1880s developed into a significant operation. There was also the smaller Nyth-y-Gigfran quarry working on the eastern cliffs of Allt Fawr. Oakeley took over Nyth-y-Gigfran in the late 1880s, connecting with the mine underground. At the same time, Cwmorthin suffered its own rockfall and in 1900 it too was taken over by and connected to Oakeley. At their peak these combined quarries produced 60,000 tons of slate annually and were the third largest in the United Kingdom.