The mound is the remnant of a fulacht fia, a type of prehistoric cooking site found in enormous numbers across Ireland, typically Bronze Age in date, and almost always positioned close to a reliable water source. This one measures about twenty-six metres north to south and twenty-three metres east to west, rising just thirty centimetres above the surrounding ground, modest dimensions that are entirely typical of the form.

A fulacht fia works on a straightforward principle: stones are heated in a fire, then dropped into a water-filled trough to bring it to the boil. The shattered, blackened stones that result from repeated heating and cooling are discarded into a mound beside the trough, and it is precisely this accumulation of burnt and fire-cracked material that survives in the landscape long after the wooden trough and the fire itself have vanished. At Derrishal, ploughing has disturbed the edges of the mound and spread that burnt material across a wider area, roughly sixty-six metres north to south and forty metres east to west, which gives some sense of how the site has been gradually eroded over time. A second fulacht fia lies approximately two hundred metres to the north, a pairing that is not uncommon; suitable spots near water attracted repeated use, and clusters of these sites across a single townland are well documented elsewhere in Cork and beyond.