Clifford Park is a challenging place to ride. Lots of singletracks, many not refelcted on the map, some quite difficult. It has a reputation as a freeride haven but there are a lot of more mellow trails too. 

Expect to discover about 8 miles of trails when you fully explore the place.  Located right in Biddeford it's extremely popular with local riders.  This Strava map suggests the frequency that the trails are ridden and offers clues to some nearby riding too.