I know nothing about them myself. There could well be a scientific/archaeological basis for it, but once, eh, enthusuaists start talking about 'spiritual' powers related to some site or concept, the archaeologists/scientists tend to avoid the whole thing like the plague.
Quite so, very sensible of them. But... there's a book called The Experience of Landscape
by Jay Appleton (Wiley, revised edition 1996, ISBN 0-471-96235-X). It starts from the question, "What do we like about landscape and why do we like it?" I've never managed to finish the book, but have heard others who have speak of it. The thesis appears to be that since humans evolved as hunter-gatherers, the landscape is very much the arena in which life happens. The ideal landscape consists of a location where one can look out for potential prey and
for potential predators, with somewhere close by to rapidly retreat to in the case of the latter. He calls this idea Prospect-Refuge-Hazard theory. No way to prove this, but it seems to make sense, and would indicate a deep and emotional relationship with the landscape would be likely. That might be the stimulus for 'spirituality' notions.
Which means it's nearly impossible to find out what's really the case. Wikipedia is disputed and doesnt really have very much info, although it is interesting to read what the dowsers have to say about it [In the 1930s, two British dowsers...]- I grew up in a town in the west of Ireland, but in the surrounding countryside dowsers were used to find a location for a well. From what I heard they would even be able to tell how deep you'd have to go. So I have great respect for dowsers...
The Wikipedia article does justice to Watkins, as far as I read him; it quotes him from other sources than The Old Straight Track
I haven't heard much about dowsing recently, but it works well enough to be at least semi-respectable. My former boss is a Ph.D and a very good scientist and technologist; he found it worked for him on at least one occasion. It's been mentioned in New Scientist
magazine, albeit not (I think) for a long time. The last speculation I remember seeing was that dowsing is a naturally-occurring form of nuclear magnetic resonance in the brain.