Need to make reservations. How do I do that?

Online or show up early enough to claim an un-reserved camp site; assuming there are any remaining available. https://www.parks.ca.gov/?page_id=555

Try Stanislaus county par k s and recreation dept/reservations. Or drive on up there. I visited there a few days ago and there where lots of campsites available. Very nice camp hosts. So much fun!

We didn't make a reservation. We just drove up there and met with the campsite person onsite.