x2 on the site above. Only link you'll ever need.
Yes, the forest service roads are legal to drive on, unless posted otherwise. But if it's an active logging route, tune the CB channel and listen up - you do NOT want to be on the trail when those logging trucks come rolling down...you will lose.
And it will be awhile before the snow melts, but there are enough roads under the snow line that you should be good if you head out. If I can't make a trip far enough north or south to get on a real trail, I'll hit I-90 and look for an open fire road to explore with a few friends on occasion. Sometimes you find a great trail, and sometimes it's a bust. But even when it sucks, it's still exploring in the Jeep, so worth the trip.
In fact, if you are in North Bend, head out towards Garcia and McClellan Butte. NF-9020 and NF-9021 don't have the full loop open right now, but plenty of places to hill climb. Be careful though if you get around to the south side - LOTS of loose flat rock, and it gets slick. Stay in the mud this time of year.
And in a shameless plug - drill down close enough at maps.live.com (2 miles or less) and you'll see most of the forest service roads.