First-come, first-served campground. My friend and I stayed outside the park on a Friday night, then got up early Saturday morning to come stalk these campsites at 6am. We circled around for a bit, accidentally drove over a large rock, sat there looking defeated, then some nice woman came up to our car and told us they were leaving soon. We were so thrilled to get a site! Set up our stuff, then went to hike Cloud's rest.
The evening however was pretty annoying. Like the reviewer before me, we were next to some large family get-together, around 15 people, playing music and making a racket. there is definitely NO ONE enforcing quiet hours. I always being ear plus so I was able to fall asleep…but it was definitely the opposite of a peaceful night in nature.
So…just bring ear plugs. And watch the rocks if you're driving a low-clearance vehicle.
Found one last spot that seemed like a great site. Ended up being next to a group that cramped 20+ people on one site, drinking and yelling until two with a huge lantern that lit up everything around it. It was like I was camping in the middle of the day at a frat house. No sign of any ranger to enforce the so called "quiet hours" of 11PM. Packed up at 5AM and went to Yosemite Creek instead.