There are quite a lot of cairns in the surroundings. Some of them are just clearance cairns, some are genuine burial cairns. It is not easy do be sure about these sites and hard to find information to clear up doubts.
The 2 cairns on my pictures are on the summit are a few hundred metres W from the Harbourne Head Menhir. I measured them about 23m in diameter and they are 20m apart from each other. The eastern cairn is the more prominent one of the two.