I don't think they sign up for trails anymore. You just show up & go.
There was only one trail they were particular on last year. It snaked down into the woods, crossed a small creek, up a pretty steep & loose dirt track trail covered in pine needles. It was 75 yardsish long. The bypass was just as bad. It was very offcamber.
When it rains (it rains every year), the difficulty goes up a degree, just like at the offroad parks.
The obstacle course is the funnest part of the entire event, IMHO.
The trails are great to get in the woods & find some shade.