Geology of Colorado (Boulder Valley) - Field Trip #1, Stop #3: Fountain & Lyons Formations

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Note tiny white and gray pebbles sitting on sand dune surface.  These are called "lag sands" and are evenly spaced on the surface.  Caused by wind blowing pebbles along and breaking them up some as they bounce along.  This even spacing only occurs in dune deposition, not river.
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Note tiny white and gray pebbles sitting on sand dune surface. These are called "lag sands" and are evenly spaced on the surface. Caused by wind blowing pebbles along and breaking them up some as they bounce along. This even spacing only occurs in dune deposition, not river.