I want to start off by saying I was never able to check with a park ranger and ask how the overflow camping is technically supposed to work but here was my experience. I arrived at the campground around 5pm on a Friday night and everything was full. After driving around for a bit I saw signs for Overflow camping. There appeared to be two sections where overflow camping is permitted. I will post pictures of the one I stayed in over by the slot canyons and day use areas. Since my setup does not require a tent and is super easy to move around. I was able to use the camp fire rings at the day use area for dinner, s’mores, and star gazing. It was actually lovely because the noise of the busy campground was far away and I had the entire day use area to myself. Then after I put my fire out I drove back over to the overflow parking spot. If you are in a Van or similar car/suv setup this may be an option for you if the campground is full. Also, I was still able to use the showers at the campground and use the bathrooms at the day use area so that was nice :)