Usually when you arrive that late, you just pull into your assigned camp site, and just check in with the camp host in the morning. There's no gate/guard shack to the camp ground so you can just pull right in. That's what my wife and I did when we stayed last December.
Yes, but you should always check in with a camp host because he was on top of everything and I'm sure would not hesitate to kick you out if you didn't have a reservation! We happened to get there in the afternoon and the camp host was not there, but there was a table that you could check yourself in and pay if you had not done it online. However you should make a reservation online prior to driving that rough road because they will sell out.
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