That bears an uncanny resemblance to Welsh Gorsedd circles, used to mark Eisteddfod locations. Are they druid associated by any chance?
This is the Gorsedd circle in Fishguard, 'planted' in 1936
and this one is in Bute Park, Cardiff, 1978 I think
Neither of them megalithic therefore but presumably based on the real thing.
We have examples of cromlechs and dolmens in our local vicinity, this one is probably the best example at Pentre Ifan (Evan's Village), North Pembrokeshire
Will have to have a think about how to get the MG near for a photo op