I am on a first name basis with this single mom! The little guy should be about 3 - 4 months old. Every other hike or so I stumble into these guys and about 3 - 4 months ago the calf was minuscule. Now he is half her size so he is growing pretty fast. They eat straight of the Aspens and also grass, not sure what else.
The pictures were taken on the way back home between Creole and Quittin' Time. Here they are (click to enlarge):