Geology of Colorado (Boulder Valley) - Field Trip #1, Stop #5: Lykins, Canyon Spring, Morrison, Dakota Formations

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A very revealing image. The horizontal cross beds coming in from the left of the picture are truncated by the diagonal cross bed coming from top left and proceeding to bottom right. The sand dunes shifted dramatically, thus truncating the previous layers. Right at the contact point, you can see "lag sand" (tiny pebbles) which are transported and broken apart in high winds in the dune environment. These are precisely the winds that cause the shift in the dunes.
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A very revealing image. The horizontal cross beds coming in from the left of the picture are truncated by the diagonal cross bed coming from top left and proceeding to bottom right. The sand dunes shifted dramatically, thus truncating the previous layers. Right at the contact point, you can see "lag sand" (tiny pebbles) which are transported and broken apart in high winds in the dune environment. These are precisely the winds that cause the shift in the dunes.