Cut through by a modern drainage ditch, it has inadvertently revealed what lies beneath: a dense layer of heat-shattered sandstone fragments packed into charcoal-dark soil, the unmistakable signature of a fulacht fia.

Fulachtaí fia are among the most common prehistoric monuments in Ireland, found in their thousands across the country, yet they remain genuinely enigmatic. The prevailing interpretation is that they functioned as cooking sites, probably from the Bronze Age onwards. The typical arrangement involved heating stones in a fire until they were intensely hot, then dropping them into a water-filled trough to bring it rapidly to the boil. The shattered, fire-cracked stones were then discarded into a mound nearby, which is precisely what has accumulated here at Tomboholla. The site takes the form of a D-shaped rise, roughly 11.8 metres along its longer axis and about 0.6 metres high, positioned at the base of a north-east-facing slope and close to a stream or drain, water being a fundamental requirement for this kind of activity. Where the field drain cuts through the straight northern edge of the mound, a section some 0.4 metres deep of fractured angular sandstone in charcoal-rich soil is visible in the exposed faces, offering a rare unintended cross-section through the debris of ancient use. A solitary hawthorn grows on top of the mound, a species with a long association with old earthworks in Ireland. Roughly 100 metres to the south-west lies a ringfort, a type of enclosed farmstead typically dating from the early medieval period, suggesting that this particular corner of Mayo has seen sustained human activity across a considerable span of time.