Those whoop-de-dos are natural believe it or not....well, i guess the process was started by the wear from dirt bikes and jeeps but water and weather did the rest. They go on for many miles on some trails. they aren't done intentionally.
Jeff
Unfortunately I'm ashamed to say no, not natural. Exactly like a washboard road traveled by cars, the whoops are formed by the long travel suspension of legal enduro bikes during an enduro event attended by upward of 300 riders. Because of wetlands and other sensitive areas, regulations requiring the route to use roads combined with the sandy soil these whoops are formed, thus you are correct in that that they are man made, but NOT intentionally. Unfortunately the enduro clubs were not required to drag the roads after the event when they were soft, now they're hard and permanent.
I'm fairly familiar with the area and believe the others have figured out your route. At the military gate after turning around, a couple hundred feet you turned onto Burnt Cabin rd, then onto Shamong rd then onto Oswego rd, past Cutts cranberry bogs where the pipe gates are. Oh yeah the old turkey farm that is now a protected snake den area where that cable gate is on Oswego rd. You then made your way out to Harrisville Lake? Nice area to explore, be cautious with some of the water hazards, you have the right truck, expect to have a quality Piney pinstripe at the end of the day. Many of the roads are to overgrown for your truck. The area is still very active but not by trucks as was in the 60's and 70's, reason why many roads are overgrown.
As for why the Forest service "destroyed" Allen rd. Many have been asking that very question with no definite answer.
I have a theory, the intent is to limit the public by making the road miserable and allow the road to revert back to nature. There are many other sand roads to get to the same place, but not quite as convenient.