The opening faces south-south-east. To a casual eye it might read as a natural rise in the ground, but it is almost certainly the remains of a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, particularly in low-lying or waterlogged ground.

Fulachtaí fia, the plural form, are among the most common field monuments in the Irish archaeological record. They typically consist of a crescent or horseshoe-shaped mound of fire-cracked stone and charcoal-rich soil, the accumulated debris of repeated use over long periods. The working principle, as far as archaeologists understand it, involved heating stones in a fire and dropping them into a water-filled trough to bring the water to a boil, possibly for cooking, though theories about their use have ranged from food preparation to dyeing cloth or even bathing. The characteristic horseshoe shape develops because spent, shattered stones were raked to the sides of the trough and left to accumulate over time. The site at Carriganass fits this profile closely, its dimensions suggesting a well-preserved example, and its south-south-east opening aligning with the typical pattern in which the trough would have sat at the open end of the mound.