G- As long as you are on private land, with the owners permission you are OK. When you get onto public land then law says anything over 100 years is "historical", and most agencies have rules for anything over 50 years. You can supposedly look at it but must leave it (unless a coin or something like that). Arrowhead collecting on public land is now a no-no.
Good luck on contacting the other owner, and hope you get permissin to MD the properties, no telling what may turn up.