Oh I don't know, I'm a local girl and if you'd asked any of my family, older generation friends about the Roman mining remains at Charterhouse just a few miles away they would know them intimately, they would recognise the spot you were describing if you talked about the Priddy barrows, they could talk at length about the Saxon palace at Cheddar, or finds in Cheddar Caves, but I only got to know about the henges through books - I don't think they are as well known as you might imagine locally (although I'm sure plenty of folk do know...). That said, I can't imagine anyone living on the land itself, buying the land or managing the land could possibly not know 'something' interesting was in their field