In AZ you have to be very careful. If you get near an ancient indian site you can get in big trouble.
In the parks you can really only look for recent stuff like coins and jewelry dropped by campers and hikers. Sometimes the park's website will tell you if detecting is allowed. I have heard that many rangers don't like metal detectors so they will tell you that you can't even though certain detecting is actually allowed.
Thanks for a great link, it was very helpful... I travel around the country alot & often wonder where I can metal detect. Atleast now in the state parks I can look it up quick. Chris