since you're in Gaithersburg, Take 118 West until it ends at Rte 28. Turn right at 28, you can go all the way to Point of Rocks MD, very nice.
Or you can veer left off of Rte 28 onto 107 towards Whites Ferry. Go through Poolesville all the way to the Ferry.
Alternately you can make a Right onto Clopper (117) from 118 towards Boyds. At the stop go straight onto Whiteground. Follow out to 28, turn right, turn right again at Bucklodge, and take that back to 121 Clarksburg Rd. Make a left on 121.
For local roads those are pretty good. Anything around Sugarloaf mountain (off of Comus Rd.) should also be pretty nice. SOme paved some gravel.