It measures roughly five metres north to south and six metres east to west, and to a passing eye it would register as nothing at all. But that dark, charcoal-rich soil is the residue of repeated, purposeful burning, carried out here perhaps three or four thousand years ago by people whose reasons remain, as with so many of these sites, a matter of educated inference.

Burnt mounds are among the most common yet least discussed prehistoric monument types in Ireland. They are typically interpreted as the byproduct of a cooking or heating process in which stones were fired and then plunged into water-filled troughs to bring the water to a boil, a method known from experimental archaeology to be surprisingly efficient. The shattered stone is the direct consequence: thermal shock splits rock that has been heated and rapidly cooled. At Ballynamona, this deposit survives as a band of charcoal-rich material roughly twenty to thirty centimetres thick, sitting about twenty centimetres below the topsoil, and is visible in the cut faces of a drainage channel that crosses the spread to the north-west of its centre. A relic drystone field wall, running east to west, also crosses the mound slightly north of centre, suggesting that later agricultural activity passed over and through the site without fully disturbing or recognising what lay underneath.