Howdo Barry
Sorry to disappoint you fella but Hagg means a scrubby type land e.g covered in gorse, I think it comes from the old Danish. There's quite a few Haggs type places up on our moors. The adder is also known as the hagg worm in north yorks which coincidentally is also the same in Norway.
Gerrick Moor is a crackin place with tons of earthworks, unfortunately it was knocked about a bit by the army charging tanks over it in WWII.
If you drop me a line at fitzcoraldo at hotmail dot com I'll send you some ideas I've been putting together regarding the goddess on the moors
cheers
fitz