As I suggested in that post, the slight mound in the field at SN 124358 is most likely to be a heavily degraded Bronze Age burial mound. It is approx 25m across, and appears roughly circular, and it sits on the highest part of a little plateau, with glorious views in all directions. The field is well drained, and here and there one finds fragments of foliated rhyolite on the surface. If the field was to be freshly ploughed, broken fragments of this rock would predominate, together with bits of dolerite. Both rock types are seen in the hedgerows round about. The geological maps suggest that foliated rhyolite is the bedrock type here, just as it is a short distance away at Rhosyfelin.
There are many other Bronze Age burial mounds in the area, especially on the summit ridge of Preseli -- for example at Foelfeddau, on Foel Cwmcerwyn, and on Foel Drygarn. There is another one at Carn Briw, not far from Carningli. They seem to be preferentially located on hill summits or plateaux. Should we call these features round barrows? Possibly not -- they are generally too small, although some of them contained cist graves before they were vandalised by ancient antiquarians.
As I suggested earlier, the mound in the field near Pensarn might well have been much more prominent originally, but after many centuries of erosion and maybe deliberate and accidental destruction by animals, ploughing etc, there is nothing much left. A guess is that it was maybe 10m in diameter and maybe 3m high originally, and that it has now degraded down to this very low feature with stones and soil spread out to a diameter of c 25m. Another guess is that it is made of smallish rhyolite and dolerite stones collected locally -- although there may be larger slabs in the core.
Kate Welham has suggested that "something big" might be discovered here. What might that be? Well, the hope is that proto-Stonehenge will be found here, either in the form of a circle of monolith sockets or maybe in the form of some monoliths still embedded in the ground which can conveniently be labelled as "the ones they left behind." How likely is any of this? Plenty of foliated rhyolites and dolerites will be found, either as small slabs or cobbles or as larger boulders, pillars or slabs. The archaeologists will want to call any of the latter larger lumps of rock orthostats or monoliths, but they will have to be very careful indeed about that, since the landscape was, and is, littered with very large stones as a consequence of glacial and periglacial action during the Devensian cold period. Large numbers of such stones have already been removed -- you can see them where they have been "liberated" and relocated into hedge banks or used as gateposts in farms including Rhostwarch, just down the track: