Keep an eye out for mountain bikers.
This trail system is well maintained, well traveled, interconnected, and easy to follow but is mostly unmarked.
It's about 5 miles of multiple twisting, winding singletrack trails around Naylor Mill Park. Relatively flat (there are many technical obstacles built for the mountain bikers that use the trail). The trails utilize one ridge for as much climbing/descending as is possible. The trails are very compact with many switchbacks, but make the most of the forested area along Leonard Pond Run.
Even though you can run each section of the trail separately they are all interconnected at the beginning of the trails near the back northwest corner of the Naylor Mill parking lot. You can turn north or turn south and run a section of the trail or run one trail into the next. The path you see in this posting is using both the north and south sections as one long trail.
The southern section starts off flat and winds around towards Naylor Mill Road and then descends down toward Leonard Pond Run (waterway) and you'll start to experience some climbs along the run. The northern section is a slightly longer run that is more flat as it winds its way around the forested area back to the parking lot.