It is a cupmark, one of those shallow, circular depressions, typically ground or pecked into rock by prehistoric people, whose precise purpose remains unknown. This one is modest in scale, just six centimetres across and six millimetres deep, but it is well-defined and intentional, occupying the eastern side of a subrectangular sandstone outcrop that measures roughly 1.6 metres east to west and 1.2 metres north to south.

The decorated surface itself is small, only about ten centimetres in either direction, and faces gently southward. Immediately to the west, a natural hollow sits in the same rock, a quirk of geology that raises the familiar question in prehistoric rock art studies of where the natural ends and the human begins. The outcrop lies within an area of scattered boulders and rock exposures typical of upland Kerry, and the broader landscape around it has a particular quality. To the north-east, the Behy River valley opens up in clear view, while a horseshoe of mountains wraps around from the south-east, through south and west, and back north, enclosing the site on most sides. Whether the cupmark's makers were responding to this topography in some way, or whether the placement was incidental, is one of those questions that survives the millennia unanswered.

Cupmarks are among the most widespread and least understood features of the prehistoric landscape in Ireland. They appear on exposed outcrops, on the kerb stones of passage tombs, on standing stones, and in seemingly unremarkable upland locations like this one. Isolated examples without associated carvings or monument contexts are particularly difficult to date or interpret with any confidence. What can be said of the Kealduff example is that it is well-preserved, clearly worked, and set within a landscape that would have been navigated and used by people for thousands of years.