Sierra Buttes trail. I have not run Poker Flat (we considered it though). Easy enough to turn around. Tight trail at that point but I could back up and turn around my TJ without issues. Please note that the part I'm referring to is just the spur up to the tower where, eventually, you have to park and hike up to the tower. The rest of the trail should be passable (we approached from the north side so I can't speak to the southern portion with the switchbacks coming up from Sierra City, CA).