Midnight at Jumbo Rocks

by Joe Schofield

Title

Midnight at Jumbo Rocks

Artist

Joe Schofield

Medium

Photograph - Photography

Description

Joshua Tree National Park. Jumbo Rocks.

In 1936, President Franklin D. Roosevelt set aside 825,000 acres of California desert as Joshua Tree National Monument. The park was later reduced to 560,000 acres. However, Congress passed the California Desert Protection Act of 1994 that expanded the park to 794,000 acres and raised its level of protection to National Park status.

Geology Tour:
The oldest rocks in Joshua Tree National Park are 1.4 to 1.7 billion-year old metamorphic rocks.
These are the original rocks that the magmatic intrusions traveled up through, heating and altering the surrounding rocks as the hot material migrated. The metamorphic rocks in Joshua Tree National Park are divided into four different subunits. The oldest is called the Joshua Tree Augen Gneiss. This rock was previously granite, an igneous rock that you may have heard of if you have ever shopped for countertops. This granite was subjected to high pressures and temperatures which caused the minerals in it to migrate into bands. Small, eye-shaped structures in the rock called augens formed alongside the mineral bands. On top of the Joshua Tree Augen Gneiss is a rock unit referred to as the metasedimentary suite of Placer Canyon. Metasedimentary means that before metamorphosis, this rock was sedimentary. It is mainly composed of the minerals quartz and dolomite. The next rock unit is another augen gneiss, which is found at Monument Mountain and can be recognized by its dark color and large crystals. Last is another metasedimentary unit of the Pinkham Canyon. It contains several different types of rocks: quartzite, schist, granofels, and dolostone.

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December 20th, 2023

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