These are Bronze Age copper mine adits, horizontal shafts driven into rock by people working roughly three thousand years before any written record of the place existed. The tunnels are partly water-filled and choked with debris, but their dome-shaped roofs and the faint green staining left by copper mineralisation are still visible, as are the traces of fire-setting, a technique in which fire was lit against the rock face to heat and fracture it, allowing the stone to be broken away by hand.

A radiocarbon date obtained from the site and published by W. F. O'Brien in 2003 places the mine at approximately 3,230 years before present, placing it firmly in the Bronze Age, the period when copper ore was being extracted across parts of south-west Ireland to be combined with tin and cast into tools and weapons. The three adits are separated from one another by two natural pillars of rock and vary slightly in dimension, the largest reaching around three metres wide and two metres high. Immediately north of the cliff face sits a large, irregularly shaped spoil mound, roughly fourteen metres east to west and nearly two and a half metres tall, now mostly covered in sod. Where its northern edge is actively eroding down toward the river, the material inside becomes visible: heat-shattered stones, stone mauls (rounded hammerstones used to pound and break ore-bearing rock), nodules of charcoal, and dark soil stained by centuries of burning. A second copper mine lies approximately forty-five metres further north, suggesting that this particular stretch of valley was worked with some deliberateness by whoever understood the geology well enough to find it.