When the site was physically inspected in 1984, the ground told a different story: no fortress, no earthwork, but a quarried section cut into the eastern end of an esker ridge running through pastureland.

Eskers are long, winding ridges of gravel and sand deposited by meltwater streams that once ran beneath glaciers during the last Ice Age. In the Irish midlands and west, they were valued for centuries as natural causeways across boggy terrain, and the gravelly material within them made them practical targets for quarrying. At Mullagh, the ridge runs east to west, and it is at its eastern tip that the extraction activity took place. How the placename Caislean-na-Cirche, with its suggestion of a castle or enclosure, came to be applied to what is essentially a worked-out gravel feature is not recorded, though misreadings of quarried or eroded landforms as defensive earthworks are not uncommon in older cartographic practice.