They move them around depending on the water level. This year all of them were on the middle fork lined up about 200 yards apart from each other. Last year we had number 5 it was in a large cove directly across the main part of the lake from the dam with one other campsite about 200 yards away.
I will second they are bigger than that picture may lead you to believe. The main 2 story structure is 20' X 24" with a bathroom a storage area,a full size picnic table, a sink (no running water), and a barbecue. We had 2 large tents on the second story.
There is also an additional "platform" that they have added in the last few years that is about 6' X 20' where you can hang out and put out a bunch of chairs and tie the boats off to. We easily fit 12 people and chairs on this with room to spare.
Link to map of the lake with locations of the sites where they normally are at high water level.
http://www.parks.ca.gov/pages/462/files/LakeOrovilleMAP.pdf