Hi Pat,
In my experience this happens every once in a while, if the rangers
don't get there to open it up. I have the rangers' number in my cell
phone (it's posted on that bulletin board in the park), so I ask
around if anybody's called the rangers yet and call them myself if
nobody has. The last time it was locked, the rangers explicitly told
us to just park by the side of the road and walk in, if we wanted, but
I'm a little too paranoid about tickets to take that as a general
rule.
- WG