Oh, it might be just arrowheads...since game animals are there, could have been used as hunting grounds. Then places like that also could have been used for ceremonies. There is or used be websites about rock piles used by Native Americans. I'd have to do a search first to see if those sites are still around. Sometimes referred to as a "sanctuary in the woods".
The red Xs I got about 2 feet deep, except one 3 ft depth. I thought at first they were caches, started checking to make sure the signals were not coins in old cellar holes. I get treasure, but want to be sure, if caches or not. Any placer gold on your property?
I have some metal detectors, you don't just walk into a city park and dig holes. Having a detector allows the treasure hunting activity in such places. You can dowse the spots your detector beeps before digging. I've used dowsing to pinpoint beeps instead of pushing the pinpoint button on the detector.