White sands with
mountains in the background
So, we have an enormous amount (275 square miles) of white sand in the
middle of a desert.
HOW DID THE SAND GET THERE?
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
(See the light layers in the mountains in the top picture.)
HOW DID THE GYPSUM END UP HIGH UP THERE IN THE MOUNTAINS?
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:
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)
WHAT'S SO SPECIAL ABOUT WHITE SANDS?
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.
Geological Overview of White Sands National Monument
by S. G. Fryberger.
Geology Fieldnotes provides you with many links to additional
And here is the
Geology of Sand Dunes by John
This 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
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
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
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!