W6pea, state beaches, all up and down CA, are routinely detected, and no one's ever had a confiscation or a ticket. If you're in San Diego, you no doubt see others plying the beach with detectors, right?

Detecting state-of-CA owned beaches has simply gone on here, since the earliest days of detecting. So it's just never been questioned I guess. Even right in front of rangers of all different ranks, no one cares.
The supposed rule, that his supposed superiors, could morph to apply to you (cultural heritage type stuff) have never been applied. It's probably better to keep it that way, and not ask, lest it occur to someone "gee, I guess I better tell you no".
There was one close call incident at a state beach in my area though: a state archaeologist just *HAPPENED* to arrive at a particular beach, to do some sort of lecture talk at a little beach museum they have there. It was just a fluke that he happened to glance out to the water's edge, as he was getting out of his car to go into the building, and saw a friend of mine hunting. The archie came down and gave him the riot act. The friend of mine posted about his encounter on a particular CA forum, and of course, we all thought the archie was nuts, because it's just a simple fact, that the beaches are routinely detected all the time. So a few people thought maybe "we should straighten this out", and "prove this guy wrong" and other such solidarity fight-back type reactions. But a problem developed: the more and more you look into the matter (in the dusty minutia boiler plate junk in the codes), the more and more it seemed like, if someone really wanted to, there was, in fact, things that could be applied (ie.: cultural heritage, "collecting" verbage, etc....) So, the long and short of it was, we wrote that off as a fluke, and leave good enough alone. That archie probably went back to his land-locked sacramento office anyhow.
So you can see from this example: sometimes it's best to find out from the local long time md'rs to find what the
reality is.