You can no longer purchase a campsite directly from the campground. There is no longer a lottery for available sites and all reservations must be made online through reserve California.com
There was a daily lottery during the week I was there in August. There are plenty of campgrounds available so it's pretty easy to get one. Not a lot of people show up for the lottery. Most Campground spaces seem to remain empty though they are reserved with campers who do not ever show up. It's kind of a weird thing at our state campgrounds.
Not sure, but I think if you show up and they have a vacant site, you can get it.
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