I've seen concrete like that under overpasses. Infact I once watched twin boys in new matching yellow Jeep CJs cook tires up that concrete repeatedly. The flat at the top was just barely big enough for one Jeep to sit without hitting chainlink fence. Soon as one slowly snakes his way back down and the other goes up. This went on for about 2 hours.
Rich kids in a place called Camp Verde Arizona. I admit there was nothing else to do for miles around.