It's right above Yonkers, and not a big trip from NJ. A ton of great rocks to climb, singletrack, and an awesome 15 minutes loop that has a tons of rocks to climb and jump and drop off of?
You can probably link up 12+ miles of trail if you know what you are doing, but you might end up hitting some trails more than once (nothing wrong with that). The place has some real cool technical rock features, and skinnies to play on as well. The park isn't big, but it will definitely provide a challenge. Also, you are never really that far from the parking lot, so its hard to get lost.