Not all of them. In fact, I would bet the farm that it's only a tiny fraction as there are countless developed U.S.F.S. and BLM campgrounds that are first come, first served. Stayed in two of them last month in MT and rode by many more. Every U.S.F.S. campground in the area of Seeley Lake is first come, first served, and they were all packed to the gills the Friday before July 4th. Ended up getting a room. Nice relief from the 90+ degree heat.