First, there are a number of suspicious pits in the turf, too small to be quarrying excavations and generally about 2m across and up to 50 cms deep. To me, they look like stone extraction pits from which suitable dolerite boulders or stumpy pillars might have been removed for use elsewhere. Some of these pits might actually be standing stone sockets; and in two or three cases there are "leaning stones" with pits around them. On previous visits these pits have been full of water, but after a spell of dryish weather I noticed that they are full of rounded and sub-rounded cobbles and stones -- varying in size from fist-size up to skull-size. These are mostly made of dolerite, and they look as if they have been picked out from glacial deposits and maybe used as packing stones. Interestingly enough, in the pits there are relatively few fragments or shards of the "meta-mudstone" or rhyolite found on the hill summits of Banc Du and Cnwc yr Hydd.
Second, there are a number of traces of more elaborate stone settings, sometimes associated with slight pits and sometimes not. Here are three examples:
This is another more obvious ring cairn, about 40m to the SE of the hill summit and its pile of stones. It;s somewhat irregular and incomplete / damaged? The embankment is about 50 cm high, and the circle diameter is about 10 m. There are hollows, about 4m across, on its northern flank -- might they have been hut sites, or just sites from which stones have been robbed?