I think it depends on the season. In the summer peak season, when all of the loops are open, the entry kiosk is manned and there are some FCFS sites in the upper loops. Outside of the summer season, from October through April, only Loop 1-22 is open, the kiosk isn't manned, and you have to reserve through the www.recreation.gov website. You can do this same-day, but if accessing the website from a cell phone, do it before you leave Orland while you still have good cell service. As of January 2023, there is no reservation fee, which is nice; most Federal-administered campgrounds charge an $8 fee.

You have to reserve a site, but you can do it on the day you arrive. There’s little or no cell service at the site, however. We were saved by the timely arrival of the camp host who let us use his Wi-Fi hot spot to reserve the site we’d already set up in.

I think you can drive up and drive in as there is a significant overflow area should the reservations be full up.

It is reservation only, they no longer take FCFS. I think you can make day-of reservations with Recreation.gov though.

When I went, I reserved my sites. It was not busy at the time I went. I did notice people driving around. That being said, I can't find anything showing any FF sites on recreation.gov. I would advise to call their number... 530-865-4781. Hope this helps.