Bullfrog campground is located in Armstrong woods (Guerneville, CA). It's on top of a rugged drive up the woods and they are first come first serve basis. It's a close drive to the Russian river, but more tucked away from all the tourists. You can do some tough hill hikes through the Oaks or easier hikes through the Redwoods which remind me a lot of Muir Woods (but less crowded than that).