That time of yearAs sunlight begins to decrease day to day in…

That time of year

As sunlight begins to decrease day to day in the northern hemisphere, plants begin making less chlorophyll in their leaves, removing the source of their green color. Great Sand Dunes National Park in Colorado sits at elevations between 2000 and 4000 meters (7500 to 13000 feet). This picture captures the Aspen trees on the slopes above the sand dunes; along with Alaska and Canada these are some of the first trees on the North American continent starting to change color for the fall.


Image credit: NPS

On the geology of these dunes: