Winter in Colorado is a funny thing. Storms can dump feet of snow in the mountains and not a flake will reach the valley and plains. Such is the case this winter. The great part is that the feet of snow in the mountains makes for great skiing, on the slopes or back-country, whichever you choose. But if you choose to bring your dog into the woods with you, consider his safety.
A very energentic 11 month old Visla was having fun in the woods with his owners, who were on snowshoes, when a back country skier collided with their dog. Unfortunately, the dog sustained a severe laceration to his right front leg that needed immediate medical care. The edge of the ski sliced through the muscle and a nerve, cutting down to the bone. The owners were able to get him to Central Veterinary Emergency Services where the ER Veterinarian sutured the wound. This sweet dog lost a lot of blood, but he recovered well and was sent home that evening. It will be 2 - 3 months before the Veterinarian and his owners will be able to determine the full extent of his injuries and whether he suffered any long term effects from the accident.
Fortunately there is a positive ending to this story, but had his owners been in the back country when this happened he might not have faired so well.
Outside magazine has a great article that describes the steps to train your four footed friend to behave safely around you as you're skiing, but it really depends on the dog. Cross-country skiing is less dangerous, but, as some commentors pointed out at the end of the article, is still best done with a well trained dog.
The moral of the story... enjoy the great outdoors, but consider how well your dog can obey commands before bringing him along.