In the Rocky Mountain region of the United States, north-facing slopes (downhill direction is toward the north) are typically moister and heavily forested than south-facing slopes. Why

This is because the north-facing slopes release less moisture.

Explanation:

Both the south-facing slopes and the north-facing slopes receive the same amount of sun and rain, however, the north-facing slopes are wetter and forested. This is because the north-facing slopes release less moisture into the atmosphere. This allows the soil to become more humid and the environment more conducive to plant growth, unlike the slopes facing south, which release a lot of moisture into the atmosphere and therefore make the soil drier.