Fourteen metres across, it is enclosed by a fosse, a shallow encircling ditch roughly three metres wide and less than a metre deep, with a low earthen bank running around the outside. To an untrained eye it could pass for a natural irregularity in the land; to an archaeologist, it is a ring barrow, a type of prehistoric funerary monument in which a burial, typically from the Bronze Age, is marked not by a towering cairn but by this subtler arrangement of platform, ditch, and bank.

What makes the Mountrivers example particularly interesting is what lies around it. A second ring barrow sits roughly twenty-five metres to the west-northwest, and two further possible examples are clustered nearby, one about fifteen metres away and another around thirty metres to the north. This kind of grouping is not unusual for ring barrows, which sometimes appear in loose cemetery landscapes rather than as isolated monuments, suggesting the area held significance over a sustained period. Writing in 1939, the archaeologist P. J. Hartnett noted a break in the bank on the east-southeast side of this barrow, though he acknowledged it is not clearly defined and may simply be the result of more recent disturbance rather than an original entrance or feature of the design.