Today Trefor harbour is a popular place for diving, angling and other leisure pursuits – far removed from the heavy industry for which it was created. The breakwater was constructed for export of stone from a quarry on the slopes of Yr Eifl, which rises to the west. The quarry was opened by Samuel Holland, an entrepreneur from a long line of North Wales landowners, with an eye to supplying the large volumes of stone which would be needed for the planned development of Porthdinllaen (further west) as the main dock for ferries between Wales and Dublin.
The dock plan fell through when Holyhead was favoured instead. However, there was strong demand for the new quarry’s granite-like stone, which comprises porphyrite and quartz. By the mid-19th century the quarry and the associated Pentre Trevor – the village named after Holland’s foreman Trevor Jones – were prospering. The quarries at Trefor and at Nant Gwrtheyrn, on the other side of Yr Eifl, had the advantage of being beside the sea. Ships were then the main form of transport for heavy bulk cargo.
Stone was carried in railway wagons to reach the harbour at Trefor, using a cable-worked incline for controlled descent from the elevated workings. On the seaward side of the breakwater, the timber jetty for loading the stone into ships can still be seen. Similar wooden quarry jetties once punctuated the North Wales coast.
The harbour on the landward side of the breakwater became home to a busy fishing fleet as Pentre Trevor grew. Some commercial fishing continues today.