What makes those colors in the Painted Desert?

Clay Thompson
The Republic | azcentral.com
A trail from the Painted Desert Inn provides access to the badland wilderness below.

What are the metal compositions of the colors of rocks in places like the Painted Desert? The red ones have iron? The white rocks have gypsum? But what metals are in the blue ones, the green ones, the purple ones? Is copper in the green rocks?

Boy howdy, this is a bit more complicated than you think. It’s certainly more complicated than I expected.

I could run a full explanation of the geology of the Painted Desert, but they’d probably have to skip the funnies to make room for it, and nobody would want that.

The Painted Desert, which is part of Petrified Forest National Park, is millions of years old and made up of several geological layers. Over the ages, it was home to all sorts of lush plant life and animals.

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A lot of the terrain is made up fluvial deposits — stuff left behind by ancient seas and rivers. Most of those deposits are sandstone, which can come in many colors, depending on their age, erosion and the climate at the time in which they were laid down.

Some of the Painted Desert’s rocks contain iron and manganese, which can oxidize into reddish colors. However, when the water table is high there is less oxygen in the ground and that turns those deposits blue or green.

This goes on and on. I suggest you go the Petrified Forest’s website — www.nps.gov/pefo — and read more about how the park was formed.

And if you’re really interested in Arizona geology, I suggest the “Roadside Geology of Arizona” by Halka Chronic.

E-mail Clay at clay.thompson@arizonarepublic.com.

PHOTOS: Petrified Forest National Park