It measures roughly 16 metres long, nearly 16 metres wide, and rises to about 1.4 metres at its highest point, with an opening of around 2 metres facing west-south-west. What fills the mound is not soil or rubble in any ordinary sense, but accumulated burnt stone, the characteristic signature of a fulacht fia.

A fulacht fia is a prehistoric cooking site, typically dated to the Bronze Age, though examples span a wide range of periods. The usual arrangement involved a trough, often timber-lined or cut into the ground near a water source, which would be filled with water and then heated by dropping fire-cracked stones into it. Repeated heating and rapid cooling caused those stones to shatter, and over time the discarded fragments built up into the distinctive horseshoe-shaped mound that survives at sites like this one. The opening in the mound corresponds to where the trough would have sat. At Copsefield, the proximity to a stream about 15 metres to the west fits this pattern precisely, since a reliable water supply was essential to the whole process. The mound's heavily overgrown condition suggests it has seen little disturbance, which in archaeological terms is something of a virtue, even if it makes the site hard to read from the surface.