i posted this on the mtbr forums earlier. check out pt reyes...we've bike camped at sky camp and coast camp, even though there are trails that are required to access the sites, the trails to the campsites aren't too long, so folks can still access the campsites by car via foot fairly easy. the climb from the beach back up limantour rd is steep, so you might wanna pack light. wildcat camp is the most remote, haven't been there yet.

willow creek (russian river) is semi primitive, the campsites are only accessible past a locked gate. the best sites are the furthest ones down the road, they're closer to the river.

henry coe is definitely worth checking out, pretty remote for it's proximity to silicon valley...we've bike camped out there before, it's definitely what you're asking for, but super duper.....steep. bring a water purifier, filter, or tabs. watch out for mountain lions and bring your bug spray.

a couple of weeks back we rode from the monterey bay area (where i live), down to big sur, up from kirk creek, thru hunter liggett, over to arroyo seco. there's hiker biker sites in big sur, but there's cars on the road. once you get to hunter liggett, no cars, basically all the way to arroyo seco, dirt rd. you can out and back thru arroyo seco and there's definitely backcountry access into the east side of the ventana wilderness if you wanted to ditch your bikes and explore, get a map. if you really wanted to explore a bit more on bikes on dirt, check out los burros rd and coast ridge rd. definitely a nice range on this ride from ocean to redwood forest, high coast range chapparal, huge valley oaks, and steep mountain wilderness.

you might also want to check out butano and big basin state parks, you can camp at each park and ride back and forth, or point to point. if you can find a legal primitive dirt rd where you can camp w/out riding road in the greater bay area besides coe lemme know, cause i'm looking for it too. most of the places we go are mostly stealth camp spots.

what kind of bike are you riding? hopefully something with gigantor floaty tires. if you can get a chance try calling jeff boatman, he makes/designs the carousel design works bags, i believe he lives in sonora and has tons of information about off road adventure bikepacking on forest service roads and trails in his local area of the sierra (if you do please share). if you're in oakland have you explored mt tam or mt diablo? pretty sure you can ride mostly dirt from oakland to mt diablo. have fun.