That map reference must be out by a couple of digits (maximum). But it's shown in the right person's field and is broadly correct. It's on the high point of that flank of Grey Nag - I would guess 505m. This is what makes it special - the views from there reach to the mountains of the Lake District, to the south, and to the mountains in Scotland as well as the Cheviots, to the north. There is a special hill downward, and about a mile away - the north-south meridian passes over this hill and through what is putatively the centre of the circle.

I'd like to hear the Station Field Earthwork, Alston, explained. It can be fround from the picnic spot on the South Tyne Trail just past Alston Station. It's listed as Iron Age defensive but only has a front, and a grand entrance, but no sides or back. The scale is very similar to Mayburgh Henge - nobody has seen this either ...