Inspired by "Arrival" I have a feeling that some of the "ancestors" had been contacted and advised to stick up megaliths with some consideration for their descendant's ( c. 1900- 2100 AD ) technology and ocularcentrism .
If you got out a bit more you'd know what the truth really is out in the field.
Here's an idea - I wonder if we could organise the burying of some peoples SLRs and then see if a dowser can find them.