[...enigmatic” cup marks carved into their surface...]
Aren’t those panholes (a depression or basin eroded into flat or gently sloping cohesive rock.)? Notice there are no markings on the portion that was in the ground. I guess I should stop digging up and moving the boulders in my yard because a neo-lithic American might have sat there in the past?
As long as you don't post a video about it.