This cute little creature is not a mouse (or any type of rodent), but more of a miniature rabbit. It's a Pika, the smallest member of the hare family. Pikas are relatively uncommon creatures to spot - you're more likely to hear their shrill "eeeeek" cry than to see them.
Pikas have a thick grey-brown fur coat, rounded ears and almost no tail. They measure less than 6 inches and weigh less than 8 ounces. The American Pika we have in the Rockies is a solitary creature, though different species form colonies.
Pikas live at higher elevation, usually in rock piles or scree where they nest in spaces formed by the irregular piling of rocks. This particular pika was found at the base of a cliff near Lake Louise known as the Crag, close to the trail leading to the Plain of Six Glaciers.
The following video gives you a closer look at a Pika, and especially lets you appreciate their shrill cry.