Southfork Trail is just that. A singletrack trail that follows the Southfork river. Just a good all around trail for just about anyone. My 8 year old rode it when he was 6 years old. But that doesn't mean that anyone can ride it cause he is a pretty crazy 8 year old. Roughly 4 miles up and about 4 down. Off and on pedalling here and there. But it has some fun singletrack, some fun roller coaster type singletrack, some technical stuff and some relatively fast sections. Great scenery along the river and if you ever wanted to go fishing, there are some great spots to fish along the way. This video was done in 2010, but we seem to ride this trail regularly cause it is close and you can bring the kids or the dog or whatever. But don't get me wrong, it is not a flat trail. I would say a green/blue type rating for this trail (compared to most of the trails up here).
Fun out and back ride. 8 miles total i think. I think my best time was just over 50 minutes from start to finish.