Trouble at State Park

We have a 50A class A, we were going camping at a state park in Kentucky. It was hot so we were running the generator w AC on. We backed into our site, turned off generator, plugged in to 30A post using 30-50A adapter. Everything was fine but the AC would not work. I unplugged, started generator again, AC worked fine. I turned off generator and plugged into 30A post again. AC still would not work. I suspected the 30-50A adapter. I used volt meter and confirmed there was 120V on both hot legs of the 50A adapter outlet. I checked my disconnect switch with volt meter, showed 120V. After further trouble shooting I finally determined that the post 30A was wired wrong. The hot and neutral leads were reversed. Looking at the outlet with the round ground lug at top the hot leg is supposed to be at 7 o'clock, neutral at 5 o'clock. They were reversed. So the 30-50A adapter was splitting neutral instead of hot. I checked the site next door, it was good. So not only were they reversed, but also inconsistent. Ranger let me move. I am stunned to think how many years it has been wrong like this. Folks with 30A rig probably would't notice. Perhaps some with 50A rig were okay too, but not me. I now have a dedicated outlet checker in the cord compartment to easily check the post wiring before I set up and plug in. Another lesson learned the hard way...