Peterson's Offroad did their "Ultimate Adventure" in NH
Linky here: Ultimate Adventure 2010 Introduction - 4-Wheel & Off-Road Magazine
BUT, it was all on private property! :-(
Evidently, most offroad sites are on private property and only accessible through joining a 4-wheel club.
I don't know of anywhere except class 6 roads from the Delormes books.
There IS an Offroad park in Granville, NY (3 1/2 hrs from Lowell, MA)
Mettowee Off-Road Extreme Park
M.O.R.E. Park & Club