School of Life Sciences | Ask A Biologist

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Anatomy of the Desert

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  • Bajada: a group of fan-shaped areas on the ground where sand is deposited, starting from a small point (usually in the mountains) and widening until they reach flat ground.
  • Caliche: a hard rock layer found under some desert floors that is made of calcium, gravel, sand, and other materials in the ground.

Water Signs

Anza Borrego streambedThe desert may seem like a barren place, with more open areas of soil surface and much less life than some other biomes. So when we look at the desert, we notice more than just the plants and animals. We also notice some peculiar patterns in the ground.

Although deserts are dry for most of the year, when they do get rain, they can get a lot. This creates all kinds of shapes and paths in the sandy desert floor. The runoff from rain creates deep, broad streambeds, called arroyos or wadis that remain dry for most of the year.

Flash flood

The Flash Flood

Sometimes, when a lot of rain falls in the desert, the streambeds aren’t deep enough to hold all the water. The water can overflow, rushing across the hard-packed desert floor in a fast moving flash flood. These floods can cover a large section of ground, moving gravel, clay, sand, and other soil particles out of the streams and spreading them out across a broad, flat area. This broad area is called an alluvial fan. Several alluvial fans can cover a larger area, creating a bajada.


Beneath the Dirt

Though water can rush across the sand in deserts, it can also soak in very quickly in some areas. However, sometimes there are unseen barriers to water below the surface. Hard patches of concrete-like material can develop inches or feet below the desert floor. 

Haboob in TexasThis material, called caliche or hardpan, is created when minerals like carbon dioxide and water interact and accumulate over time after drying out.

What is a Haboob?

Water isn’t the only driving force that moves dust or creates barriers in the desert. Huge dust storms, called haboobs, can grow to thousands of feet tall, moving soil and minerals miles across the desert. Over enough time, haboobs can even move enough dirt to create sand dunes in some areas.


Flood image courtesy of Martin Feldner. Additional images via Wikimedia Commons. Sand dunes by user Brocken Inaglory.

sand dunes

In the desert, both wind and water are important forces that shape the land. Sand dunes can be created and shaped by wind or by water.

Desert to Rainforest
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sand dunes

In the desert, both wind and water are important forces that shape the land. Sand dunes can be created and shaped by wind or by water.

Desert to Rainforest
Teacher's Guide
Download as PDF or
Get MagCloud version for print or iPad

Share to Google Classroom

Be part of Ask A Biologist

by volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteer page to get the process started.