The prehistoric feature is a burnt mound, a type of site found widely across Ireland and Britain, typically consisting of a trough or pit used for heating water by dropping fire-cracked stones into it, with the discarded burnt stone accumulating into a distinctive mound nearby. The Greenhills example was modest in scale, comprising a few pits and a rectangular trough, with a dense cluster of stakeholes on the upslope side of the trough, likely the remains of a simple working structure or windbreak.

The complication is that the original avenue leading to Greenhills House was later driven straight through the site. That avenue was no minor track; it was a properly engineered cambered road with a gravel base, and on its southern side ran a masonry ha-ha, the sunken boundary wall designed to keep livestock out of formal grounds without interrupting the view across the landscape. A drainage ditch ran along the northern side. By 1904, the avenue had fallen out of use entirely, and a ditch was cut across the area to enclose what appears to have been a rectangular garden. At the far end of this garden stood a shed of some size, its posts large and square, set into postholes in the ground. A separate area of investigation turned up a small spread of burnt mound material and a continuation of the ha-ha wall, suggesting the prehistoric activity had extended a little further across the slope than the main concentration implied.