A marker cairn shown on the OS maps is a pillar of stones raised upon an earlier round cairn on the summit of Pen Carreg Gopa.
The round cairn is a stony mound consolidated with light vegetation and measures about 8.5m across, though it appears to have partially slumped down the slopes of the summit, particularly on the north-east where it measures 1m high; elsewhere it is only about 0.3m.
The pillar of stones surmounting the cairn measures 3m across and 2m high.

David Leighton, RCAHMW, 24 April 2013