The north trail is a fun roller coaster along 3.5 miles of beautiful Salmon Creek. It is suitible for for beginning riders, but is plenty of fun for intermediate riders as well. The trail is mostly singletrack with a little dirt road here and there. The trail terminates at Salmon Creek Falls C.G. There are few obstacles (usually) and not too much poison oak.
The bridge that once connected the north and south trails was washed away during a winter storm a couple of years ago. What was a 6.5 mile loop is now a 14 mile out-and-back if you do both trails. The ride can be made longer by adding the connector trail from Greenwater Park and the trail(s) across the river from that park.
The trail on the south side of the creek is a much more technically challenging one. It is definitely not for beginning riders. It is mostly narrow singletrack over rocky, rooty, steep-pitched, wet ground. I suggest people avoid riding here during anything but the driest of weather because of the abundance of salamanders that use the trail. This trail, too, is about 3 miles long one-way.