Sandstone cliffs in the Colorado National Monument near Grand Junction, CO

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Three photos of sandstone cliffs in the Colorado National Monument near Grand Junction, CO

Sandstone cliffs in the Colorado National Monument near Grand Junction, CO. I learned from Google AI that the dark streaks and spots on the sandstone cliffs are a geological phenomenon known as desert varnish.  The varnish is primarily composed of microscopic layers of clay minerals mixed with manganese and iron oxides.

Desert varnish builds up incredibly slowly—often taking thousands of years to produce a distinct dark coating. AI noticed the bright, orange-tan patch near the bottom of this image and told me that this highlights a spot where a section of the rock recently broke away, exposing the fresh sandstone beneath before the varnish has had time to rebuild.

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David Sparks

I retired in 2005 after 40 years of research and teaching at the University of Alabama in Birmingham (24 years), the University of Pennsylvania (8 years) and the Baylor College of Medicine (8 years). Photography is my retirement hobby.

Nature photography, especially bird photography, combines a number of things that I really enjoy: bird-watching, being outdoors, photography, travel, messing about with computers, and learning new skills and concepts.  I now spend much of my time engaged in these activities.

David Sibley in the preface to The Sibley Guide to Birds wrote "Birds are beautiful, in spectacular as well as subtle ways; their colors, shapes, actions, and sounds are among the most aesthetically pleasing in nature."  My goal is to acquire images that capture the beauty and uniqueness of selected species as well as images that highlight the engaging behaviors the birds exhibit.