All of this was packed into an upper layer of black peaty silt inside a cist, the term for a box-like burial chamber typically formed from flat slabs of stone, and all of it dates back somewhere between 2460 and 2140 cal BC, placing the burial firmly in the Chalcolithic, the transitional period sometimes called the Copper Age, bridging the Neolithic and the Bronze Age.

The cist sits at the approximate centre of a cairn, a mound of stones used as a funerary monument, at Coolnatullagh. By the time excavation took place, reported by Eogan in 2002, the cist had already been disturbed and only two limestone slabs survived in place: a southern sidestone roughly 0.8 metres high and 0.3 metres thick, and a capstone measuring approximately 0.95 metres long. The excavation was carried out not as a planned research dig but to facilitate repairs to the cairn following that earlier disturbance, which makes the quantity of information recovered all the more striking. The cist itself contained no grave goods, but the surrounding cairn yielded a perforated dog tooth, a glass bead, a possible stone pin sharpener, a chert scraper, a flint blade, and several sherds of pottery. A secondary inhumed burial was found within the cairn as well, suggesting the monument was used across time rather than sealed at a single moment.

What makes Coolnatullagh quietly unusual is the layered nature of what was found inside such a reduced structure. Most of the cist's material culture was absent or removed before excavation could record it, yet the human remains that survived were enough to return a precise radiocarbon date and to suggest that this small, damaged chamber once held the dead of more than one generation, or perhaps more than one rite, within the same modest space.