Early Ordnance Survey maps, both the 1840 six-inch edition and the 1915 revision, marked it as an enclosure, the kind of hachured outline that usually signals an earthwork or fortification. It is, in fact, a nunatak, a geological term for a rocky prominence that protrudes above, or in this case once protruded above, surrounding glacial ice, left behind as the glacier eroded the softer material around it. This one measures roughly 67 metres on its northeast-southwest axis and sits at the northern end of the mountain plateau, looking out over Galway Bay.

The misreading of the site had a long afterlife. T. J. Westropp, writing in 1915, took the prominence to be an earthen construction and proposed it as a possible inauguration place of the Eoghanacht chiefs, a Munster dynastic grouping with deep roots in early Irish political history. Spellissy, writing in 1980, accepted that suggestion. It was not until Tom Coffey examined the site in 1985 that the formation was correctly identified as the eroded upper tier of the mountain itself. What Coffey did not observe, and what satellite imagery has since revealed, is that the nunatak is not entirely without human intervention: a low curving wall of around 20 metres survives along its upper northeastern edge, and a possible small cairn is visible in the northern sector. An east-west field boundary also crosses the feature, with what may be a hut site along its line. The geology is natural; the activity on top of it is a more complicated question.

The site sits at an exposed elevation with extensive views northward across the bay, which may help explain why it attracted attention, and speculation, for so long. The partial wall along the northeastern edge is the detail most worth looking for, easy to overlook and long overlooked in print.