Please define what you mean by "northern California"? Everyone has a different idea of what this is!

There are lots of no-permit (or at least just self-registration) areas. In fact most Forest Service areas are self-registraion off-season. If you want to go in the Sierra without permit hastles, go Oct-May.

Off-trail travel in the coast range is brutal to nearly impossible. Your are kidding yourself if you think this is fun! Nice little-used trails in the Marble Mountains, Snow Mountain wilderness, Trinity Wilderness. Yes, you have to get a permit. No real hassles - go into a FS office and just get one. We all have to bend a little to comply with regulations. This is also a good way to find out about the latest conditions. I find the FS personnel quite helpful.

Warner Wilderness - far northeast corner of California. Another nice area - best done early season - gets really dry and hot later. This is a small wilderness, but has challenging travel. Trails are so little used that you have to be a good tracker to find some. No permits needed.

The peaks east of the Sierra from Bridgeport to Lee Vining area are seldom used. Tioybe National Forest. It is really easy to pick up a permit in their Bridgeport office - few quotas for those areas.

Although it is farther south than you want to go, if you want a real adventure with no trails, no permits in really tough challenging country - go to the east side of the White Mountains. This is also an early-season area. Best to do right now. Once the snow melts, there is little water.

You had better be an experienced off-trail backpacker with good navigation skills to do these. I may be wrong (and pardon me if I am) but it sounds like you want "Survivor Man" experiences and are unwilling to bend politically (get a permit). Honestly, the best off-trail travel is the high Sierra. I go out for 8 days without seeing anyone. Bite the bullet and get a permit and see the best country!