During mud season, avoid the north end of the north bound Gnu loop and the dismal swamp part of the South loop. The suggested route, assuming you're riding the standard direction (see arrows on trail) is this: On the south end of the South Loop, when you get to the Gnu loop connector, take it. This gets you off the south loop just before the dismal swamp. Ride the Gnu loop to the 2-track crossing a little past the 1 mile marker. Get off here and go left (west) about a hundred yards on the 2-track to pick up the southbound Gnu and ride it backwards (north) -- that's a right turn back onto the singletrack. At the north end of the Gnu Loop, go off the end of the hairpin to re-connect with the South Loop, which is just a few yards away. You'll miss some good dry trail this way, the south half of the south-bound Gnu and the a little of the NE South loop, but you can ride those backwards and figure it all out from the map.
There is no society in recorded history that ever suffered because its people became too reasonable. Sam Harris