Okay, Dagger, I consulted the most expert source for river tripping in Northern California, my 1973 edition of
Canoeing Waters of California by
Ann Dwyer. Ann was a mentor of mine when I bought my first canoe as an adult in 1980 in San Jose, CA. She also ran an equipment business called Dragonfly Designs, which made the best rope throwbags and float bags on the market at that time, or any time. Her vinyl end bags in my MR Explorer have not deflated in 39 years. She also made me a custom made paddling suit from a then new fabric called Goretex. Also custom made square end bags and split rectangular center bags, which could abut the triangular end bags for solo position paddling.
These are easy to intermediate river runs on California coastal rivers with perhaps an occasional portage. You can find campsites put-ins, take-outs and shuttles from various online reports, articles and outfitter websites. There must be appropriate water levels. You can surely paddle these river sections faster than Ann's estimates. She liked to go slow and absorb.
Eel River. Can be run the 32 miles from Alderpoint to South Fork. Ann calls it 3-7 days.
Navarro River. 16 miles from Hendy Woods State Park to Dimmick State Park,1-2 days. 10 miles from Dimmick SP to Navarro-by-the-Sea, 1 day. This river will go through big redwoods and firs. You can continue paddling along the ocean coast if the water is calm.
Russian River. I don't know how many miles total, probably more than 80. Ukiah to Hopland is 16 miles, 1 long day. Ann doesn't list Hopland to Cloverdale, but I know class 3 Squaw Rock rapid is in that section and maybe some other rapids. Cloverdale to Healdsburg is 30 miles, 2-3 days. Healdsburg to Reins Beach is 27 miles, 2-3 days. Reins Beach to Jenner on the ocean is probably another 8-10 miles or so. Many outfitters on this river, especially around Healdsburg.
Trinity River. There are several sections of class 2/2+ whitewater, mostly pool-drop, from Lewiston to Hoopa. You should have whitewater experience. As I vividly recall being told by a voice on the telephone in 1981, "Don't go into Burnt Ranch Gorge or you will die." That, of course, was before whitewater expert Bob Foote did it in an open canoe (a Mad River ME). But lesser mortals will still die.
I did sections of all these river in the early 80's and miss them all.
You can also do day trips up and down the Big River from beautiful Mendocino, and the Noyo River from Fort Bragg along the route of the famous Skunk Train. These are redwood runs when you get far enough upstream. As tidal rivers, you will have to time your runs to catch the tide properly up and back. I never tried it, but maybe you can even stealth camp overnight when you get upstream far enough. It certainly gets wildernessy enough.