These arrowheads were most likely lying on the surface of the earth since their last use, hundreds of years ago. Of course it's possible someone had picked them up in the preceding decades, but doubtful, given people's propensity to collect. Collecting arrowheads on federal land is prohibited by the Archaeology Resources Protection Act of 1979. Take a picture, and then leave them where you found them. Or tuck them out of sight.
By leaving arrowheads and other worked pieces of appropriate rock - mostly chert and obsidian - where they were found, the next person is given the opportunity to have a magical moment of connection with the people of the past.