Death Valley 18: Geological Ages Transposed

Image Commentary

In the background the dark mountains are composed of Pre-Cambrian age metamorphic rocks (rocks that have been changed), well over a billion years old. In the forground are the light colored Tertiary age lacustrine rocks that contain much of the borax deposits for which Death Valley is so prized as a resource. These rocks range in age from 40-20 million years in age. The difference in height of the two ranges shown here is entirely appropriate; Pre-Cambrian metamorphic rocks are typically far harder and more resistive to erosion than the softer mud rocks of the Tertiary deposits in the forground.

Borax is an extremely valuable substance used in everything from detergents to chemical industries. Some 80 per cent of the USA's total reserves lie within the Death Valley National Park. Much of the human activity observed in Death Valley, particulalry in earlier days, is directly the result of Borax mining.