How to make trails into the snow in Bryce. If you have questions, send me a mail.

For making trails in snow you need Bryce and an image editing program. I've used Photoshop.
First make a terrain in Bryce. Attach a bright snowmaterial to it. Then go to the terrain-editor (the little "E") and choose the "rounded dunes"-fractal (the down-arrow next to the "Fractal"-button). Click on the Fractal-button until you have a terrain with very soft hills. Below is the terrain, I've used.
Copy the terrain-image (CTRL-C on PC's, CMD-C on MAC's). Exit the terrain editor.
The terrain-image and the resulting Bryce object.

Now open Photoshop. Make a new image (CTRL-N or CMD-N and paste the copy you've just made from the Bryce terrain image - CTRL-V or CMD-V).
Next I've used an black and white image of footprints I've prepared before. But you can use of course something else e.g. animal- or car-trails. The trail-image (grayscale-mode) should have the same dimensions as the terrain-image.
Select all of the trail-image (CTRL-A, CMD-A) go to the terrain-image.
Create a new channel and paste the copied trail-image (CTRL-V, CMD-V)
The trail-image (left) and pasted into a new channel in the terrain-image in Photoshop (above)
Now use the new "Alpha-channel" as a selection (You will see the "marching ants") and change the "brightness/contrast" of the selected parts to -25 and -10 (if you use darker values the footprints will be deeper).
Deselect (CTRL-D, CMD-D), select all again (CTRL-A, CMD-A) and copy the image again (CTRL-C, CMD-C).
In Bryce go again to the terrain-editor of the selected terrain and paste the just copied image (CTRL-V or CMD-V)
The result are footsteps in the snow which are not flat but follow the shape of the terrain. Here you can see both images to compare. The same method can be used to make streets on an area with hills.