Thanks for the replies, guys. The "trails" that I usually do riding on are probably 85% trail and 15% fireroad, I guess, mainly because they're slightly wider than doubletrack.

Yeah trekkie820, they can get pretty nasty, especially after it rains. For some reason, someone (probably the park ranger) dumped a whole bunch of woodchips onto one of these trail-fireroad thingies on one of the huge climbs and now my rear wheel sometimes spins out on the woodchips when I torque my way up.