They are the remains of a causeway that locals have long called St Senan's Road, and according to tradition, the reason it was never finished comes down to a red-haired woman who walked past the workmen one morning without saying a word. That silence was enough. The men downed tools and the road stopped where it stops to this day, roughly a mile and a half out from Carrig Island.

The tradition was recorded in 1938 by pupils at Ballylongford School as part of a wider folklore collection, and it ties the causeway to St Senán of Scattery Island, a sixth-century monastic figure associated with a small island in the Shannon estuary some six miles to the north-west. According to the story, Senán ordered a road to be built connecting his island all the way to Carrig Island, known in Irish as An tOileán Beag, or Little Island. Whether construction began during his lifetime or later, the account does not say. What it does say is that the unfinished road remains visible at every low tide. Members of the Kerry Field Club who visited the site in October 1943 noted that local people could still point out the pathway as it crossed through the fields of Carrig Island, turned east, and descended into the estuary. A second visit in April 1952 found the causeway exposed and passable on foot. The 1943 group also walked to Aughavallen, the old parish associated with Ballylongford, where they found decaying masonry and overgrown vegetation marking what had once been the road's far end. The modern bridge connecting Carrig Island to Carrigafoyle on the mainland may itself follow the line of this older crossing, though that connection is not certain.

The submerged stonework is only visible at low water, so timing matters if you want to see more than the surface of the estuary. The pathway through the fields on the Carrig Island side, which once led down to the causeway's starting point, may still be traceable on the ground, and the ruined end at Aughavallen, though described in 1943 as already well decayed, marks the other terminus of a road that local memory never entirely let go of.