Short loop, beginner/intermediate. We had to ride it twice to get in an hour ride. (Note: another map here is listed as McKeldin Area, but it is not.. that map is for an area further south.)
From Rte 70N, take the exit for Marriottsville Rd (exit 83), bear right at the split. About 5 mi, turn left and park where RR tracks cross the road. Ride left out of pkg lot onto Marriottsville RD, trail drops in on right side in about 1500 ft.
http://www.singletracks.com/item.php?c=1&i=6593