The heat rises from the ground up through the snowpack and sublimates the points off of the snow crystals at the bottom. This leaves them more rounded. Conversely, the rising moisture from the vaporizing of the snow below condenses on the colder snow crystals near the top. So ball bearings form on the bottom and the snow above becomes denser and heavier. Typically, Colorado's winters start out with a thin snowpack and below zero temperatures in the mountains.
Depth hoar is almost the rule.
North faces, where the air is colder, tend to be worse. You should know what the layers are like where you're skiing and hiking. An occasional pit and constant probing with your ski poles are about the only ways to know what's below. Be careful about probing with ski poles. A buried crust may feel like the ground.