fdl, for starters, whatever you're reading on that fmdac "state-by-state" listing, in only for state parks in those states. NOT other forms of land. There's been a lot of people who read some of those states with "dire sounding wording", and think it means "the entire state". That's not the case. The listing is only for state "parks". So for example, it would have no bearing on city and county parks, schools, land, etc... Also, not all state land is state "park" land either. The list would have no bearing on federal land, which as mountain digger points out, some forms of federal land have no restrictions. HECK, even EXPRESS ALLOWANCES, doh

(what more could you ask for?). Like BLM, NFS, etc... So it's also a myth that "all federal land is off-limits".
And a word of advice about that fmdac listing: Some of that I would take with a grain-of-salt. Sorry to say, but the reality is often different than the "dire sounding wording" that listing presents. The reason for this, is you have to take into account how such lists were compiled ........ to begin with. Here's how: way-back-when, whenever someone got ready to make a compendium reference like that, they did the obvious: they went and asked. Sounds logical enough, right? I mean ... who better to ask, than the state's themselves? Doh

For example: In the mid 1980s, the fellow "R.W. Doc Grim" who wrote the book "Treasure Laws of the United States" took on the task like this: He merely xeroxed off 50 letters, and sent them to state capitol in all 50 states, to the heads of the park's depts. in those states. The letter introduced himself as preparing to write a resource book, and asked "
what are the laws regarding the use of metal detectors in your state parks?" And Grim simply puts the answers, in alphabetic order, in his book (complete with their own letter head to show busy-bodies in case your approached, etc...). The theory being, is that now a person travelling around (RV'rs, for instance), can carry the book, and know the laws ahead of time for each state.
But now honestly folks: put yourself in the shoes of persons getting such a letter. What do you THINK the "safe" answer was going to be? Most of those states had nothing specifically saying "yes" or "no" either way. There was no mention at all (no specific prohibitions). However, that didn't stop a lot of those states, when answering, to morph something ELSE they think applies. Usually the cultural heritage stuff, or disturbing the flora, or other such nonsense. Because think of it: admittedly, in any given state, there's bound to be a few of the state's park with admitted historical themes, right? And no one would argue with being prohibited from hunting at a sensitive monument, right? But if you are the one tasked with answering such a letter, who simply can not split hairs, and say "yes at these 35, but no at these 4". Or yes at this one, except not on the golfing green, or by the historic cabin on the north shore", etc... Obviously they can't be going into great details like that. So what do you THINK was going to be the easy answer? To simply say "no", of course. Or to say "inquire at each kiosk you come to" (and then if you do that, the same psychology simply presents itself at each kiosk, when the wide-eyed clerk fields your question, doh!).
So an odd thing happened when that book (which led to later internet lists like the fmdac one) started making the rounds: There were a lot of the states that had dire-sounding wordings, or outright no's, that ......... quite frankly ..... no one had ever had a problem before. The old-timers were left scratching their heads saying to themselves "since
WHEN?"

See how that worked? It was, and continues to be, a shere case of "no one cared, till you asked".
And to be honest with you, some of those states, with supposed "no's" or severe limits, I bet you can still detect (as long as you're not being a nuisance snooping around obvious historic sensitive stuff), and no one cares. For example: A strict reading of the CA section on that listings, tells you that you must "get permission from the park office". Yet I can tell you for a fact, that you can detect state-of-CA beaches here (which is a division of the park's dept., afterall), till you're blue in the face, and never hear "boo" (and ... no .... no one "asks at each beach kiosk they come to" either

) However, I'm sure if you were to ask enough archies in Sacramento, sure, you'd probably eventually find one to scream "nneeeooooo". But as you can see, reality (barring someone being a true nuisance, or asking stupid questions of the wrong people), is often a different world.