Who's been digging in my garden...?

Now that most of my garden is clear of snow, I discovered these channels. Some little creature, about the size of a mole, I should think, has been happily burrowing away under the snow, but not under the grass, probably because the ground was frozen. The result is these channels across the length of my garden. They are all on one side, next to the field at the back and fortunately they aren't very deep. so I guess they will fill in easily. I can't say I'm thrilled with my discovery, as it has made a bit of a mess, but it is interesting all the same, don't you think?