I'm sure you're aware of the 'science' behind crop marks, but if not it's pretty simple. Walls or other impervious structures stunt plant growth, leaving a 'parch mark' above, say a wall. The greener crop marks are generally down to holes or ditches being dug, and later back filled or filling up with looser or 'humic' plant material material, which I guess is what you saw with your crop mark. The break in the crop mark ring is intriguing, and does seem to 'address' those hills in the distance, though without knowing the direction of the entrance, I wouldn't like to say.
Anyhoo, some good examples of crop marks turning up....
https://rcahmw.gov.uk/cropmarks-2018/
 Reply | with quote | Posted by Monganaut
9th July 2018ce
20:26 |
Crop marks? (thelonious, Jul 09, 2018, 14:57)- Re: Crop marks? (Monganaut, Jul 09, 2018, 16:30)
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