Measuring just fifteen metres across in each direction, it is thought to be a crannog, an artificial island constructed by people rather than shaped by geology, though in this case the builders appear to have worked around an existing outcrop of natural rock, piling stone into a cairn to create a usable platform above the waterline. The distinction between what is natural and what is man-made here has blurred entirely, and the interior is now so overgrown that reading the structure from the surface is difficult.

Crannogs were a widespread feature of Irish lake landscapes, used from the Bronze Age through to the early modern period as defensible homesteads, their isolation offering both practical protection and a degree of social prestige. Lough Carra, a shallow, limestone-rich lake in south Mayo, contains several such features. This particular example sits approximately 480 metres north of a pair of causeways, the kind of submerged or partially submerged stone trackways that were sometimes built to connect lake islands to the shore, though those causeways are separate recorded sites in their own right. D. Lavelle's 1994 archaeological survey of the Ballinrobe district, which covers both Lough Mask and Lough Carra, identified this structure and noted the ambiguity at its core, that the cairn-like accumulation of stone may have been deliberately built up around a natural rock foundation, a common enough technique that leaves later investigators uncertain where geology ends and human effort begins.