ghalt, your advice, to someone who feels they just MUST talk to a live person, to talk to a cop, is a good idea. Because they don't make the laws, they just enforce them. But I would not extend that to asking a
park personell or
ranger though. Only city cops, or sherrifs. Reason is, park personell work at the very location, instead of city-wide, like cops do. And in a way, these park personell/rangers DO "decide" what can and can't be done "on their watch". Unlike a city cop, who is dealing with violent crimes, robberies, rapes, etc... Your question will sound like you're an angel to a cop

But a park personell/ranger, whose only focus is just on the park he works at, can merely put out a "no", just because he feels like it. Yup, there doesn't even have to be an actual rule or law. He has the authority to interprett and enforce things as remote as "don't disturb the vegetation", as a reason to tell you "no". And if you fight it, the law will stand on his side, since he is an appointed agent, given that latitude to interpret rules "for the public good". And you might get a "no", when in fact, no one would've cared or noticed if you'd just gone.
Don't ask bureaucrats either. They might tell you "no", even if a rule doesn't exist (because they envision geeks with shovels). Find it in print yourself (usually available on-line at state websites key word searching), or ask a cop who really doesn't care, or have any vested interest. If the law is silent on the issue, then consider yourself as no different than any other park user.
And as for "tickets" (you mentioned), in my 30+ yrs of md'ing, I've detected hundreds of parks, all over several states, and never once asked or inquired of laws. If it's not posted "no metal detecting", and as long as it's not an obvious historical site, I just go. Sure I've had some bootings and "scrams" over the years. But no, I don't believe you'll get a "ticket", unless you were someone who couldn't take a warning, or someone night-sneaking a sensitive site, etc.... I'm sure there's some isolated incidents someone can post, of a person getting a ticket for an un-posted non-historical site, but I'd say they are the exception. Just as now and then a driver gets roughed up by an over-zealous cop for a simple seatbelt violation, doesn't mean that we should all wonder if we can drive or not.