This is a burnt mound, a type of prehistoric site found throughout Ireland, typically consisting of a heap of fire-cracked stones discarded after repeated use in a water-heating process. The mound at Knockalegan is modest even by these standards, its maximum extent roughly six metres, its edges too gradual and uncertain to be read easily from ground level.

Burnt mounds are closely associated with fulachta fiadh, a term used for prehistoric cooking or processing sites where stones were heated in a fire and dropped into a water-filled trough to bring it to the boil. The arrangement at Knockalegan is intriguing because it sits within a small cluster of related features. On the southern side of the mound there is a shallow depression, around two metres across and opening to the south-west, which may represent the remains of such a trough, though it could equally be the result of more recent ground disturbance. Two small circular rises nearby, each only a few metres in diameter, may or may not be connected. What is clearer is the broader pattern: another burnt mound lies roughly one hundred metres to the west in the same field, and approximately eighty to one hundred metres to the south-south-west there is both a further burnt mound and a fulacht fiadh. This kind of clustering, multiple sites of apparent prehistoric activity concentrated within a single low-lying, boggy area, is not unusual, and may reflect the repeated use of a landscape particularly suited to the work, with ready access to water and fuel over a long period.