For what's its worth, I can tell you first hand that in USFS Region 2 (includes Colorado) that as soon as you drop a blade (or a tiller or a compactor bar) you are moving from over-the-snow travel to either "building road" or "grooming".
We groom cross-country ski trails for a Nordic Club, and are currently waiting on USFS analysis/decision as to whether we can groom a section of road that is regularly used by snowmobiles, but is not groomed by a snowmobile club. I can travel that road in our snowcat, but using a blade or dropping an implement is whole different ballgame in the eyes of the Forest Service. This particular road is already compacted most of the winter (so from a common sense standpoint what difference does it make?) but it is the use of machine that changes the regulatory situation. If anyone cares I can go into the background, it has to do with an agreement that USFS Region 2 reached with US Fish and Wildlife Service over Canada lynx.
From a practical standpoint, I believe they might cut me some slack if all I did was knock down one or two drifts on my way in or out, or if using the blade merely to create a safe place to turn around. A threshold here is probably on the scale of something you could dig by hand (with considerable time/effort), and building a jump might be in that category, but I have no experience with the law enforcement folks on the White River NF, other than running into those guys who patrol from Vail Pass.
Are the people you've dealt with there pretty reasonable?
