I downloaded the full size picture, enhanced and magnified it.
The track is relatively fresh--the sharp angles along the left edge show that it is not significantly modified by sun, wind, or additional snow. (The little piles of snow in the left side of the track are from breakdown of the wall which appear to occur mostly on the outside of the turn.)
There is a linear ridge about 3/4 of the way across the track and there are fine lines evenly spaced every ~1/2in (assuming the track is ~9in wide). (The ridge and lines are parallel to the track.)
The closer part of the track is pretty uniform (although there are some slight indentations that might be filled-in boot prints), but there are some obvious indentations a bit this side of the log across the track. And right near and beyond the log there are a number of indentations. The edges of the track also appear to be less uniform near and beyond the log.
The tracks are very uniform--too uniform and too straight (the curve is long and gradual) to be made by an animal. IMO, it was made by a dragged, sliding, or rolling (uniform contact zone, such as a wheeled vehicle) object.
You (AndyF) haven't said anything about the consistency of the snow. The top few inches is obviously deformable powder, but is it soft below? Or is there a hard layer below. (I'm guessing a relatively hard layer a few inches down--see below.)
My first guess was skis--relatively narrow skis could create a 9-inch wide track while gliding. But skis would leave a ridge in the center and would not leave the 1/2in lines. (However, at least some jumping skis have multiple grooves--5 are shown in an illustration in one of my books.) There are no poling marks, kick marks, and the track width is too uniform. Skis would also not leave the marks near the log.
A bicycle like device would have to have ~6inch wide tires or tracks with a longitudinal tread, but no cross tread to leave the observed track. (Such a tire/track would be a bad design for traction in snow.) The front and back tires of a bike take slightly different paths (the front tire often wobbles a bit more than the back due to steering). Wheels would also leave slightly deeper and shallower sections in the track. I see no evidence of steering, tires wouldn't make the marks near the log, and the track depth is too uniform.
My best guess is a human dragging something man-made. If there was a reasonably firm layer a few inches down, his footprints might generally be shallow except just before the log and 3-4 ft this side of the log. (Perhaps towing tether length was ~3-4ft and he had to pull harder to get the towed object over the log.) A towed narrow sled-like device might fail to smooth the snow just on the other side of the log. (The suggests that he was moving toward the camera.) I can also see some faint marks in the track that might be boot prints that have been smoothed over by a dragged object.
The towed object would be ~9 inches wide with ~20 uniform longitudinal ridges along its bottom to leave the overall track with the uniform fine lines. (The uniformity of these fine lines is my reason for suggesting that the towed object is man-made.) But the bottom does not appear to be flat (or slightly convex) because it leaves the ridge in the right side of the track. What is the object? Why does it leave the ridge? My first thought was a log, but it wouldn't explain the uniform lines. It might be some sort of narrow pulk or sled, but that doesn't explain the ridge. Some pulks/sleds have runners. Perhaps a runner was missing on one side?
And, of course, the human would have had to walk fairly precisely so that the pulk/sled would travel over and fill in the tracks (except near the log).
Enough speculation for one evening...
Doug