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Geological Info

White sands with san andres mountains in the background

So, we have an enormous amount (275 square miles) of white sand in the middle of a desert.



The white grains are blown out of an old lake bed, Lake Lucero. The bottom of that old lake is full of gypsum.

More gypsum comes out of the surrounding mountains when rain or snow washes it down into the Tularosa Basin.

(See the light layers in the mountains in the top picture.)


Excellent question.

Those mountains used to be the bottom of a sea. That was way back when New Mexico was located close to the equator and the world map looked like this:

The supercontinent, Pangaea in latest Paleozoic time

started breaking apart 220 MILLION YEARS AGO


70 million years ago the Rocky Mountains were formed and the bottom of that old sea was pushed up.

10 million years ago one of these elevated spots caved in and created the Tularosa Basin. (Source)


White Sands is the largest surface deposit of gypsum in the world. How come? Gypsum exists even in large amounts almost everywhere around the globe. But it is soluble and usually gets washed away into a river or sea of some sort. Not so in the Tularosa Basin. The word basin tells you there's no river outlet. Otherwise it would be a valley.


I've seen many beaches with lots of white sands. What's the big deal?

White Sands doesn't contain any silicon. It's pure gypsum. It wouldn't be looking too good on the beach as gypsum is soluble.

By the way, that's why White Sands looks a wee bit grey when it rains. But not to worry, it doesn't rain very often here in the Tularosa Basin.



Find here the Geological Overview of White Sands National Monument by S. G. Fryberger.

Geology Fieldnotes provides you with many links to additional geological information.

And here is the Geology of Sand Dunes by John Mangimeli.

remarkable brochure gives you the entire scoop on White Sands in a nutshell. I recommend it.



What about the kind of fossils we find in the deserts of southern New Mexico?

Let the Encyclopedia of Geology enlighten you:

Many genera of chambered fossil sponges with calcareous skeletons had been included in the Calcarea, in the Order Sphinctozoa, until recently, when the polyphyletic origins of the sphinctozoans and their development principally as a structural grade were recognized.

They are now treated as a group of ‘hypercalcified’ sponges drawn from other classes.

Sphinctozoan grade sponges appeared in the Middle Cambrian, but played a minor role until the Carboniferous and Permian, when they helped to produce massive reefs, such as those in the Guadalupe Mountains in western Texas and south-eastern New Mexico, and in Tunisia and China, and during the Triassic, when they were similarly involved in the construction of reefs in what is now the Alpine region of southern Europe.

They were thought to have become extinct by the end of the Cretaceous, but a living form was discovered in 1977.

There you have it. Think reef.

And now it makes sense that the fossils that you find in the desert here look like the bottom of a sea bed. Here's an example:

Fossils in Southern New Mexico
Click image to enlarge


If you like fossils you will like northern New Mexico where they have plenty of dinosaur fossils. Southern NM? Not so much. But we have White Sands. So, no complaints.


And here is the Physiographical map of North America:

Physiographical Map of North America
Click to enlarge




To the best of our knowledge all information is current. If you should discover any errors, however, please let us know. Thanks!




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