I would suggest getting some 4x4 guides from 4x4now.com, particularly the Wells guides. Here is a short list of favorite camp spots in Northern California, #1 being best. ALL of these I have attended atleast once and never saw another person, most I have never seen anyone at all.
1. Fordyce Waterfall Campsite, before 3rd water crossing. BEST CAMPSITE IN THE US WITH NO COMPETITION. Extreme 4x4 trail with extreme scenery. Camping is on a penensula with 75' X10' waterfall in front and 50' waterfall behind!
2. Briggs Cabin, Paniment Valley, free, hot showers and endless cool stuff.
3. Buck Island Lake, Rubicon Trail.(getting ruined, may be closed)
4. Mirror Lake, Mirror Lake Trail near Shaver Lake. VERY NASTY hill getting out, but fun. Awesome Fishing.
5. Summit Lake, Dusy Trail, lovely high altitude lake.
6. Unknown Lake, Kavanaugh Ridge Trail near Bridgeport. EXTREMELY high, covered in snow all year, with nice trees to block wind, camp on water.
7. Coyote Lake, Coyote Lake Trail, challenging fun trail, one very hard spot. GIGANTIC high Mountain Lake.
8. Grouse Lake, Swamp Lake Trail. Cute little Lake camp right next to water.
9. Ershim Lake, Eshirm Trail, nice, Dark, remote lake.
10. Mt. Wilson, short 4x4 trail with views of ALL of Lake Tahoe. Surprising to see open.
11. Snake Lake, Snake Lake trail. Scary but fun trail off scenic Gold Valley trail system. Lovely Lake, camp west side.
12. Rubicon Springs, Rubicon Trail, several nice spots despite being used alot, go when not crowded. Large water crossing site is best. Only pay campsite on my list.
13. River campsite far south end of Slickrock trail. Awesome waterside camp. Easy to get to from south.
14. Tuba River Camp, start of Fordyce Creek Trail, large, awesome river. Right off I80, but you cannot here the traffic.
Anyhow that enough of that...I could add good mentions for Barrett Lake, Hell Hole, Russels Camp, Geologists Cabin, Salien Hot SPrings, Swamp Lake, Strawberry Lake, Brewer Lake........The list is endless. That is why guide books can help to narrow things down. Also attend X gatherings to find these amazing places in a safe, fun environment