They are fulachta fia, a type of prehistoric cooking site found in considerable numbers across Ireland, typically beside water sources. The standard interpretation is that a fulacht fia functioned as an outdoor cooking place: stones were heated in a fire and dropped into a water-filled trough, bringing it to a boil. Over time, the shattered, heat-cracked stones were piled to the side, forming the horseshoe-shaped or oval mounds that survive today. The term is an old Irish one, loosely meaning "cooking place of the deer" or "cooking place of the wild", though debate about their precise function, whether for food preparation, textile processing, bathing, or something else entirely, has never been fully settled.

The three sites at Brownstown were identified during fieldwork in 1987, arranged in a roughly east-to-west orientation across the valley floor. The westernmost of the group sits on ground that is notably flat and saturated, fed by numerous streams and springs. That waterlogged character is entirely consistent with how fulachta fia tend to be sited across Ireland; proximity to a reliable water source was not incidental but essential to whatever activity was taking place. The linear arrangement of the three mounds, close together but distinct, raises questions that the landscape itself does not easily answer. Whether they were in use simultaneously or represent activity returning to the same stretch of valley at different points in prehistory is not recorded.