Re: California- Breaking the law, when you aren't breaking the law.
sheesk, in the current climate of parks NOT ONLY being closed at dusk, or other such rules to "keep order", there are supposedly certain cities in the USA (fortunately none around here that I know of), that ban md'ing too. So in light of how some of those cities, and nearly all state and fed stuff gets their feathers ruffled about "cultural heritage" and "archie" stuff, we should just be happy that it's only about closing at dusk, no booze, no dogs, and other such rules.
When in parks, I mostly like to detect at dusk or even night, JUST to avoid busy-bodies. With that in mind, I'd like to add a psychological point to these park hours rules: Yes it's true that a lot of "parks have closed at sunset" type signs. But you'd be surprised how many of them are only enforced "upon complaint" (or upon incidents such as yours). For example, I live in an upscale side of my city (the kind of neighborhood where people call the cops when they see suspicious persons, cars, etc...

) And right across the street from me is a small upscale park, with ...... yes ........ the obligatory "closed at sunset" sign. However, there is practically always someone dilly-dallying around there after dark. Like teenagers making out, or just someone still using the playground equipment who didn't leave at sunset, etc... And yet it is only when my neighbors and I suspect kids drinking beer, or punk-type people, that we actually have called the cops. And then yes, they come and tell whomever "park closed, beat it!". But I'd venture to say that if a cop were just on his rounds, a kid on a swing-set would not even garner his attention.
In other words, I believe that some of those "close at sunset" type signs are merely tools, for when needed, upon complaint (or if you had a REAL bored cop with nothing better to do). Sort of like noise ordinances: No one cares, or goes out with decidal measuring equipment, UNLESS the cops get a complaint. Only then do they pull out their decibal measuring devices, and go check it out. I am very aware of this d/t I have a street sweeping company, and our blowers make a LOT of noise

A few times we'd get noise-complaints, so we'd have to re-route certain shopping centers, or just be sure to go half throttle at particular hot-spots, etc... But one time, legal things went a bit further, and someone, who still wasn't satisfied with our attempts to appease them (changing times for his neighborhood shopping center etc...) went and got some public official or cop or something to measure the sound of a back-pack-blower on full throttle. That official determined that
technically this device was breaking the noise ordinance law ANYWHERE in town after 10pm (and not just on that one complainers street). We eventually got out of that legal tussle, by pointing out that blowers don't necessarily run at full throttle. Ie.: in the same way that your Honda Accord may do 100 mph, but that doesn't mean you will ever DO 100 mph

We got away with that logic, and the complainer eventually went away with other forms of appeasement.
But the reason I bring that up is, it struck me as odd that technically we had a piece of noisy equipment that was (when run properly and cranked) afoul of laws all the time. Yet we'd gone, and still do, years and years with no problem. But the minute someone calls the cops, then yes, the ordinance provides backing, for a benchmark or whatever. So I feel that it's the same for a lot of these park hours things. A lot of them are merely tools for cops to boot someone who is a wino camping out, or thugs playing their boom-box late, etc...
I'm not advocating breaking park rules, but I will say, that I hunt parks all the time at night. And to be honest with you, I never even look at those signs. I can only recall two times, in 30 yrs, that I was ever told "scram d/t park closed at sunset". And those incidents was the same as yours: that they were there for other reasons. One was because the particular park had a problem with homeless drunks thinking they could camp out in a particular park, so they'd recently upped random patrols. The other was I think because they were there on other business, and just happened to see me. In the latter incident, they actually asked me "what are you doing?" When I told them, they just shrugged their shoulders and prepared to drive on. But then he hit the brakes, backed back up, and said "the park's closed now, you gotta git". Almost as if it was an after-thought for him.