Eureka Valley Sand Dunes
The Eureka Valley Sand Dunes are located in the southern part of Eureka Valley, in northern Inyo County in eastern California, in the southwestern United States. Although covering an area of only 3 square miles (8 km²), the dunes rise approximately 680 feet (207 m) above the surrounding valley floor, making them one of the highest dune fields in North America. Eureka Valley is a basin and range structural valley oriented northwest-southeast and enclosed by the Last Chance Range to the east and the Saline Range to the west. The Eureka Dunes themselves are located in the southeastern most tip of the valley and trend north-south, parallel to Last Chance Range. According to a USGS survey map, the surrounding mountain ranges contain rocks that date back to the Mississippian and Cambrian periods while the surficial deposits on the valley floor are made up mainly of alluvium dating to the Quaternary period. They are also classified as booming sand dunes, one of only about forty worldwide.
Accessed via a gravel road in Eureka Valley (which connects to a road running from Big Pine to the Grapevine section of Death Valley), the dunes became part of the Death Valley National Park as part of its expansion in 1994. Foot travel in the dunes is permitted, but vehicle access is prohibited. A primitive campground is located at the north end of the dune field.
The Eureka Dunes are an example of a complex-linear dune- the main ridge is a static linear dune but there are active star dunes formations superimposed on the linear dune  A linear dune has alternating slip faces on opposite sides of the crest. This means it both sides of the dune have similar slopes and wind must have come from both the northern and southern ends of the valley. Star dunes have "arms" radiating off of a central crest that change direction as the wind direction changes. Little is known about the past of the Eureka Dunes and its development. The sand source is unknown, although some scientists believed that it originated from an ancient lake at the northern end of the valley.
The unique booming characteristic of the Eureka Dunes is caused by the relative motion of moving sand grains. The sound has been compared to moans, hums, drums, and, in the case of Eureka, a distant propeller plane. Most researchers agree that the average sand grain size should be smaller than 300 µm, well-sorted with no dusty material, dry and in low humidity, loosely packed, and each sand grain should be spherical and smooth  The booming sound occurs when a sheet of sand avalanches down the slip face, exciting the sand grains. The friction between these grains creates an acoustic air wave that emits an audible sound.
The Eureka Dunes are the home of several unique (and protected) plant species. The Eureka Dune Grass (Swallenia alexandrae), the Eureka Evening Primrose (Oenothera californica eurekensis), and the Shining Locoweed (Astragalus lentiginosus micans) are only found in this area. Visitors to the dunes may also experience other unique aspects of these dunes, other than the booming. In wet weather, patterns can be seen in the sand that reveals the diverse sources, and the complex Aeolian process by which these dunes are formed (and re-formed- sources and processes that are not yet fully understood.
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- Media related to Eureka Dunes at Wikimedia Commons