The advice about KNOWING BEFORE is correct. The thing is, not only CA state parks, but many other State's parks do not allow weapons. I believe you can't have a weapon in a Federal park (campground) either.
You can't blame the LE Rangers for approaching you with their weapons drawn. In today's world there are people out there who will shoot at a LE Officer who approaches them without first finding out why. I find it curious as to what you might have done if only one or two LE Rangers approached you with weapons drawn. What you did was the correct response to ANY LE Officer who orders you down. It is for everyone's protection, not just theirs. A major reason is if you are a crazy and starts shooting, innocent people could be injured/killed. They don't want that.
The advice of knowing the state laws that you are intending to visit before you get there may well save you a lot of money. By the way, even a CCW permit won't fly in many stat/national campgrounds. Weapons are pretty much excluded.