Woody, you mentioned Nose Dive as having a double fall line. I havn't been at Stowe in many years, but I seem to remember that Goat at Stowe did, too. As I recall, it was very narrow then and went down and to the left and my combination of long skis (Head Vectors 215s) and not enough talent made it pretty exciting.
Right, Bill! I provided my photo of Nose Dive because I'm not good enough on skis to *look* at Goat, let alone ski it. Bet it was plenty hairy on your Head Vector 215s.
"Our lives begin to end the day we become silent about things that matter."
Now back to the topic at hand...there was (maybe still is) an old adage that the fall-line is path a ball would take if released and let to roll down the slope. So, as stated by many above, a double fall line would be a slope or trail that "leans" to one side as well as sloping downhill.
So double fall line is a misnomer. There is only one straight way down hill on any slope that you are on. Of course this constantly changes as you move to a different spot.
Maybe a better term would be Deceptive Fall Line.
Not necessarily, because, if you are on an area where there is more than one "way down". In other words, say, you're standing in a specific spot on a trail and you "drop the ball" to your right, it will "roll down the fall line" in one direction. But if you "drop the ball" to your left, it will "roll down another fall line" in a different direction.
Jaws of Death at Mt. Snow, is another "tilted" trail. I think this is true for most double fall line trails, definitely for Jaws, that if you want to keep a straight line, one of your turns (ie either left or right) will be much quicker than the other.
I enjoy a double fall line trail, in that it is more interesting to ski than a completely flat, smoothed out groomed trail. Like many here, I enjoy trails that follow the contours of a mountain, enveloping the rolls and undulations rather than smoothing them out, including double fall line trails..
Stowe has a "better" example of double fall, the upper part of Goat.
I grewup skiing at Hidden Valley east of Pittsburgh. They have a trail, under their current twin triple chairs that has a terrible double fall line. If you simply let your skis go with the flow (gravity), in less than 100 yards you'd be in the trees on skier's right. So every 50 yards while going "down" we'd fight gravity and angle skier's left.
I was on that trail in Jan '08. Believe it's called Stingray. I can appreciate a weird corkscrew black diamond as much as the next guy, but let me tell you green and easy blue trails with wicked double fall lines like Stingray are about as much fun as pushing a lawn mower sideways across a real steep yard of grass.