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Geology of Mojave National Preserve: Kelso Dunes

Kelso Dune Sand - Where did it come from?

Wind ripples

Sand is made up of minerals and tiny pieces rock that were once part of another, much larger rock. Over time, the slow processes of weathering and erosion can turn large rocks into sand. Geologists can often track down the original source for sand grains by comparing the minerals and other characteristics of the sand with rocks in mountains nearby.

Most of the sand grains you'll see at Kelso Dunes are made of the light colored minerals quartz and feldspar. These grains were probably eroded from granitic rocks in the San Bernadino Mountains and transported eastward by the Mojave River.

Kelso Dunes with magnetite and amphibole on their crests

A closer look

Sand with gray quartz, white feldspar, and black magnetiteAs you explore the dunes take a close look at the crests. Very fine sand grains of black, iron-rich magnetite tend to accumulate on the surface. Amphibole is another black mineral you can find here. It's easy to pick out the magnetite from the amphibole by dragging a magnet across the sand. As the name implies, magnetite is magnetic.
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