A fulacht fia, the term used for these ancient burnt mound sites found widely across Ireland, typically consists of a mound of fire-cracked stones and charred material surrounding a water-filled trough; stones were heated in a fire and dropped into the trough to bring water to the boil, most likely for cooking. The Rinnaseer example came to light in May 2014, not through any planned archaeological investigation, but during routine pre-development testing ahead of the football pitch's construction.

The site sits at the edge of a west-north-westward facing slope, next to a natural basin of peat overlying marl, the kind of waterlogged, low-lying ground that fulachta fiadh tend to favour. When excavators reached a depth of between 0.3 and 0.4 metres, they found an irregular spread of blackened soil and heat-shattered rock covering roughly 12 metres by 6 metres, with occasional charcoal throughout. About a metre to the south, the outline of a subrectangular trough measuring approximately 1.7 metres by 1.2 metres was visible, though it had been filled with re-deposited subsoil and broken rock, making its precise original form difficult to read. The site had seen earlier disturbance too: a trench cutting across the north-west side had displaced burnt material downslope, leaving two smaller scatters of debris to the west. The excavation, carried out under licence 14E0144 by consultant archaeologist Richard Crumlish, did not fully investigate the mound before it was sealed in place. A second burnt mound sits approximately 50 metres to the west-south-west, suggesting this stretch of Mayo landscape was a place of some repeated prehistoric activity.