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USA - NY to LA - 2001

Another view at Natural Bridges National Monument

This whole canyon is full of arches and bridges that you would expect were carved out by a river or maybe the wind. There is no river there today in any case.

There were lizards running about all over the place. They didn't seem to mind the heat at all.


The highway took us south through Utah's Valley of the Gods, down a steep
mountain and through Monument Valley in Arizona. We are on our way to the
Grand Canyon of the Colorado.

Elephant Feet

Why is the desert multicolored?

A good question. I had no idea but have recently learned the answer. The color is often made up of a varnish deposited by bacteria.

Illustration from New Scientist

These little bugs literally paint the desert. They live in colonies on the surface of rocks and apparently like it hot. They extract energy by oxidizing tiny quantities of metals such as manganese, calcium and barium. These minerals are blown in on airborne dust and in the debris falling whenever it rains. The varnish varies in color depending on the mineral available at the moment. Over the years it builds up in layers which can be read by scientists. Possibly even be used to date geological happenings and to guess what the weather was like in the past. The oldest varnishes are about 100.000 years old and are about 200 micrometers thick. When they get that thick they tend to chip off and the process starts all over again.

All this according to an article in New Scientist 10 Nov. 2001

© Ann Thulin © Lars Thulin,
© Per Thulin, © Ingrid Hansson
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