Here is a link to the Nordic Ski Trails at Bretton Woods. Trail #36 is called the B&M Trail and may follow the old grade uphill. i found the grade back in 2002 where it crossed the Base Station Rd just below the left turn to the shops and about where the National forest parking lot entrance is on the right. The remains of a trestle may still be in the woods just below the shops.
Bretton Woods Nordic Ski Trail Map
Back in 2008 they tried to run a ski train that winter skiing from halfway down the 100ft wide row they own. Lasted only one year but made for some unforgettable photos. it was 10 deg that day,