For areas that allow mountain biking you can get a great listing for all of New Jersey at the website for the Jersey Off Road Bike Association. If you are into mountain biking this is an organization that you should belong to. Some of our regional favorites include:
The Tourne Park in Boonton
Mahlon Dickerson Park
A little further Northwest is Mahlon Dickerson Park located on Weldon Road in Jefferson. Mahlon features a wide variety of trails from advanced beginner to expert level. The Cycle Craft Bulldogs lead a Saturday morning ride here-usually biweekly.