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Geology of the National Parks - Death Valley

 

Death Valley geology field trip

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Father Crowley Point

Father Crowley overlook
Photo courtesy of Marli Miller

Valley view

If you're entering Death Valley from the west, the lookout at Father Crowley Point is a perfect place to get your bearings. The overlook is situated high above the valley floor, with a spectacular view of the park.
Ripplemarks on Death Valley Dunes
Ripplemarks on Death Valley Dunes. Photo from NPS archives.

Ripples and dunes

Once sand begins to pile up, ripples and dunes can form. Wind continues to move sand up to the top of the pile until the pile is so steep that it collapses under its own weight. The collapsing sand comes to rest when it reaches just the right steepness to keep the dune stable. This angle, usually about 30-34°, is called the angle of repose. Every pile of loose particles has a unique angle of repose, depending upon the properties of the material it's made of.

Dune formation diagram

close up of Jurassic Aztec Sandstone crossbedding The repeating cycle of sand inching up the windward side to the dune crest, then slipping down the dune's slip face allows the dune to inch forward, migrating in the direction the wind blows. As you might guess, all of this climbing then slipping leaves its mark on the internal structure of the dune. The image on the right shows sand dune structure preserved in the Jurassic Aztec Sandstone at Lake Mead National Recreation Area. The sloping lines or laminations you see are the preserved slip faces of a migrating sand dune.

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