It measures roughly 16 metres long, 25 metres wide, and about 1.5 metres high, and it has clearly been turned over by the plough on many occasions. What it represents is one of the most common yet quietly puzzling monument types in the Irish landscape: a fulacht fia, sometimes called a burnt mound.

Fulachtaí fia are generally interpreted as prehistoric cooking sites, though some researchers have proposed additional uses including brewing, hide-working, or bathing. The basic method involved heating stones in a fire, then dropping them into a water-filled trough to bring the water to a boil. The cracked and shattered stones were then discarded, building up over time into the characteristic mounds of dark, burnt material that survive across Ireland in the thousands. The association with marshy or waterlogged ground is typical: reliable access to water was central to the whole operation. The Garranes example fits this pattern closely, sitting on the edge of wet ground where water would have been readily available to whoever used the site, likely during the Bronze Age, when these features were most commonly in use.

The repeated ploughing noted at Garranes is a reminder that many such monuments survive only partially, their upper layers disturbed or spread by centuries of agricultural activity. The mound is still visible, but its present irregular shape likely reflects that long history of disturbance as much as its original form.