Joining the Hunterdon and Somerset sections may be ALMOST possible by way of the trans-continental gas line. The Hunterdon section (map link -
http://www.co.hunterdon.nj.us/depts/parks/guides/trailmaps/Sourland.pdf)
shows an exit point on Ridge Rd. Turn right on Ridge, follow down a mile or so to Lindbergh, turn right, follow Lindbergh less than a mile (just past the old hub-cap/tire junkyard), turn left on S. Hill (which I think is a dirt road), and follow a mile or so until you cross the gas line (it should be an obvious clearing with a jeep trail). Turn right, and follow across Montgomery Rd and Long Hill Rd, after which you'll enter the Somerset section.
Fair warning... sections from Long Hill down to the park entrance in Hillsborough can get very wet and muddy, especially in Spring... Be prepared... it's still a blast... On your way down check out the new trail, the 3 Amigos (about 100 yds before the fence on the right, just across from the orange-blazed post)... That will take you down to Roaring Rocks on a really awesome trail.
I also have a hunch that you may be able to connect to the gas line from Lindbergh Rd... I'm just not quite sure how (and I may be totally wrong). At least you can reach it from S Hill, and the road link on Ridge, Lindbergh and S Hill roads ain't too bad.
It would make a nice "mutant" loop (on a 29er or really any rigid MTB) ... Ride up to Rileyville by road, then take the Hunterdon Sourland trails, road link, gas line trail and hook into the Somerset Sourland Trails back to Montgomery... I may have to put my theory to the test...
Go explore.
Peace,
BB
