By the time these had appeared, I was already in possession of my FOCC (Friends of China Camp) Annual Pass - available here - of course, the first few times I hit the trails, the pass was sitting safely on my desk at home... thank goodness I had a smartphone image of it on hand.
Paying for these trails brings up a host of thoughts, of course. But, with the recent California budget crunches, one of the options which was being considered involved closing State Parks. Which pretty much sucks. And is probably reasonably unenforceable for a lot of geographical reasons. I mean, if you have no one on the payroll to patrol the park, how are you going to keep people out? Fencing is not cheap, and would probably cost more than the operating budget of most parks.
What happened at China Camp State Park has been reasonably well documented - here's an early article from 2012 in the Marin IJ - http://www.marinij.com/novato/ci_19931946 - and the newest edition of marinbike.org's Pedal Press has a decent overview article starting on page 10 (pdf download).
But it comes down to a pretty simple test - the trails are open, accessible and funded.