Tree Root Mystery in the Mountains

Sunday I came across something that I consider to be rather unusual.  When in the Bighorn Mountains of Wyoming, I was checking out what wildflowers are popping up (mostly buttercups, pictured above).  Then I noticed something odd:  Something had scraped the top surface of some roots of a tree. 

My first thought was "Could an animal have done this?"
Or perhaps, could a human have done this?

This wasn't an area where snowmobilers frequent.
If the Forest Service had been dragging some timber across the ground, perhaps that might have caused this.
However, it was only one spot and only one tree.

I found this information on the internet:

"Voles are small rodents that live underground and feed on vegetation. They are often confused with moles who feed on insects and invertebrates. Voles are vegetarian and will dine on the underground stems and roots of your plants when their usual forage is scarce during the winter. The damage to roots can kill smaller plants, but large vegetation such as trees can usually withstand vole nibbles. Voles will also chew on the bark of trees and eat into the surface seeking the nutritious cambium. 

Voles and Roots

• Tree roots are composed of hard tissue with the same vascular structure of which the main stem or trunk of a plant is comprised. The cambium is just under the surface of the root and carries nutrients and plant sugars up and down the tree. This means the cambium is rich in minerals and carbohydrates, making it attractive to the voles. When the season has become cold and herbaceous plants are scarce, the animal will forage on tree roots as a food source."
  

Indeed, the Bighorn Mountains do have voles:

Bighorn Mountain red-backed vole (Clethrionomys gapperi, undescribed taxon)
Widespread in the Bighorn Mountains



Bighorn Mountain water vole (Microtus richardsoni, undescribed taxon)
Water voles are extremely rare on the Bighorn Mountains. 

Black Hills red-backed vole (Clethrionomys gapperi brevicaudus)   

Here is a link to a coyote and a vole.  The vole manages to escape:

http://www.thatcutesite.com/brave-vole-battles-a-coyote-and-lives-to-tell-the-tale.html 

One last photo of the scraped surface tree roots.  It was a long winter with the snow having begun to melt only beginning this weekend.  I didn't look close enough to see if there were any teethmarks on the roots.  However, if something heavy were dragged across the roots, it would seem that the ground also would have been scraped and plants pulled up.  That wasn't the case -- the plants growing around the roots are undisturbed.