I couldn’t make out whether the additional small cairns were prehistoric in origin... in the same manner as, for example, those beside Pumlumon’s great Carn Hyddgen cairns? Coflein doesn’t appear to mention anything, however.
The cairn has been ‘hollowed out’ – as, sadly, you would expect – containing an OS trig station within. Nonetheless, it remains a substantial monument with far-reaching viewed towards the wilderness of Cwmdeuddwr.