This trail contains easier wide sections with hard pack dirt (especially near the overlooks). However, the trail before reaching Bootjack spring is steep switchback with large(r) rocks that will slow most runners considerably, but this section is only 1/4mile or so before the spring.
All of the trails at Gambrill State Park begin at the trailhead parking lot on the east side of the park road about half-way up the mountain between the Rock Run and the High Knob areas, on the right side of the road.
Pick up this portion of the Black Locust Trail across the street from the parking and head towards the High Knob area for scenic views of Frederick, MD. Follow the black blazes to Bootjack Spring and then retrace steps back to the parking lot, or continue along the black/green trail to the black/green/blue trail to make a loop back to the parking lot.
See the featured run: Gambrill State Park Loop
for more details on the full loop.