What is Desert Varnish?

Below is a transcription of the above sign found at the Valley of Fire Visitor Center.

An interesting feature found in the Valley of Fire and other desert areas is a dark stain on exposed sandstone walls.

In some places, this “desert varnish” is continuous and uniform, while in others it forms long ribbons.

Varnish occurs when iron and manganese present in the rock interact with water and living organism such as algae or fungi.

Scientists do not agree just how these different components happened.

Desert varnish provided a natural blackboard for prehistoric artists whose symbols speak to us across thousands of years.

In Vally of Fire, prehistoric people seemed to prefer these varnished rock faces to write on.

The designs show up clearly when pecked through the dark surface and look much like chalk marks on a modern blackboard.

Category: Sedimentary

Time Period: Cenozoic Era

Composition: Mineral and organic

Location: Exposed sandstone outcroppings