Fog drifts past fall foliage in this view of a mountain valley in the Blue Ridge Mountains of western North Carolina. Fog is a cloud that comes in contact with the ground and forms when the difference between temperature and dew point falls within a certain range. The valley is dominated by blueberry shrubs, a relative of rhododendron and azalea, which turn crimson in autumn. The Blue Ridge Mountains are part of the Appalachian chain and exceed 2, 000 meters in height.