Biked to a local park with a "primitive" hike-in camping area. No one at the booth, but it said to set up camp and a ranger would be by. Because we were on bikes, we rode directly to our campsite, and we were the only one in that section of the park. I imagine what happened was that the ranger came as far up as the parking lot, saw no cars, and figured that section of the campground was empty. No one ever came by our site. We stopped at the booth again on the way out, and it was manned, so we tried to pay. They got really confused about trying to put a transaction in the system for a day that had already passed, and said, "Never mind."