Self Check-in when the office is closed

I know parks have different systems for self check in. PA State Parks Have a listing on a bulletin board of the sites that are already booked, so make sure you choose a site that isn't booked. Just because it's empty doesn't mean it isn't taken. I showed up after dark to a site I had booked on line 6 months earlier, only to find someone in my site who didn't know the system. He just picked one that was empty. Had a fire going and his tent set up and everything. He wasn't thrilled when I asked him to please move, but I didn't really have much choice. There weren't other sites that would accommodate my trailer. That's WHY I booked that specific site 6 months prior.