When you say that the state rule in your state is to ask at each individual park you come to, I presume you're getting that info from the state-by-state alphabetic list, right? ie.: this: http://www.fmdac.org/parks/parks.htm
If so, CA has something similar to that as well: "inquire at each kiosk you come to, blah blah."
I wouldn't even call that admonition a "rule", when you think of it. Because to my knowledge, they're not written anywhere, except on the very list you're reading that on. In other words, I don't think you're going to find that in a "law" anywhere, that says, for example: "metal detectors must check in at each park for permission", etc.... Instead, where those statements came into being, was that ...way-back-when..... whenever someone got ready to make such a listing like those, they did so by asking. Yup, like send out a letter to each of the 50 state's park's dept, heads and asking: "what are the rules regarding metal detectors in your state's parks?" Sounds like a great idea, right? I mean, who better to ask, than the states themselves, right?
And as you'll notice, when/if you go down that list, and click to see more detail for each state, that rarely is/was there ever actually any rules that specifically ever said "no metal detecting". Go figure, the advent of detectors wasn't realistically till well into the 1960s, for common hobbyist usage. So in the absence of any verbage on the subject of "metal detectors", whomever receives such an inquiry, would search too and fro to find other things to morph to apply to the question. You know: verbage about "collecting and harvesting" or "taking". Or "disturbing the vegetation" or "cultural heritage" and so forth. And then they come back with dire sounding answers, or out-right no's. (when in fact, prior to that, perhaps no one ever cared or had any problems, eh?)
But a lot of them as you see, had that "ask at each kiosk" type answer. I believe THAT was born out of the following reality: In any given state, there's no doubt bound to be certain of their parks with an admitted historical theme (ie.: historic monuments). Whereas perhaps the other 90% are just run-of-the-mill beaches, non historic monuments, etc.... But whomever is answering the question obviously can't go into super detail like "yes at these 75 parks, but no at these 13, etc... So instead the easier answer was "ask at each kiosk". And notice that was never law anywhere, till now that you asked, and someone's "safe answer" got published on your nifty list. So what happens now? MD'rs read that and are now a steady stream of persons who up inquiring at the kiosks (afterall, that's what the nifty list tells them they must do). And you have wide-eyed bewildered rangers now fielding this question of 'can I metal detect?" (as if it's somehow inherently evil and in need of approval). And you can almost GUESS where this is going to go. What do you THINK that kiosk clerk's easy answer is going to be?
I wish, that way-back-when, whenever/whomever had put together those lists, that they had done so with a look-it-up ourselves approach. We'd have had a lot less "no's" and "inquire at each kiosks" than we do today.
