Not sure what your skill level is and I only know of Gambril and the Watershed in Frederick area. They are pretty technical trails and prolly not the best to start back up on. I do know of some decent trails down the road where I live in Germantown. Schaeffer, SRT, and Seneca Greenway trail are pretty nice trails for the beginner or intermediate level. Go to the mountain bike trails section of the this website and you should find what your looking for.