I've not seen it in the real, but it's got to be a natural feature.

In the absence of any prehistoric finds (flint scatters etc?) in the immediate vicinity, the only two things it has going for it that would warrant accusations of prehistoric significance would be it's proximity to Gilsland Spa (in a Goffikesque holy-by-association kinda thing), and it's position at what is roughly a prehistoric boundary between the west and east sides of the north Pennines/Cheviots.

Having said that, I'd argue for it having a place on tma, 'cos I've got a thing for the possible significance natural features may have had to our ancestors.