There's not much challenge but the singletrack is very good as it circles St. Mary's Lake.
Just after the start take a quick right and cross over a bridge then turn left heading towards the dam. Take a left at the singletrack trail at 1 mile. Cross another bridge and make sure you're on the white trail. At just over 2 miles take the left turn. At 3 miles there will be another fork - go right. Continuing forward, staying left and cross 2 bridges. At 5.1 cross the creek - no bridge here! Continue following the trail crossing several more bridges. At just over 5.5 miles stay on the left continuing on the same trail. At 7.1 miles you will turn right at an intersection heading back to the parking lot.
How to get there:
Head North on Route 5 from Lexington Park or South on Rt. 5 from D.C. Exit at Camp Cosoma Rd and follow signs to St. Mary's Park. Once in the park, drive to the far side and park by the bathrooms. A sign marks the trail
Trail open March through November. End your day with some fishing if you want.