It's a symptom of a disease called cytospora canker. Aspen trees grown outside of their rightful home in the mountains are notorious for getting it. Cytospora is opportunistic, meaning it generally attacks trees that are already being stressed in some way. The disease spores usually enter at a wound, a bad pruning cut, or lawnmower damage. There's no cure for cytospora, but some of the experts say keeping drainage cleaned up may help curb the spread of the disease.
Little holes are the calling card of a downy woodpecker.
Wounds like this can be an open door to cytospora or a number of other infections. Problem is, trying to scare away the woodpeckers might scare away the songbirds we enjoy. Damage to roots is one of the leading causes of problems to trees and shrubs, and I think that's what's happened here. I had a sprinkler system installed last summer, and I think the trenching for the sprinklers damaged some of the roots for a little pine. The roots of pine and spruce trees grow in a spiral, so it's not unusual for root damage on one side of the plant to show up on the other side.