The area within Joshua Tree National park has been undergoing changes for at least 1.5 billion years. Two widely separated episodes of mountain building has produced the results we see today. The last of these episodes was followed by an uplift period and deep erosion, and then additional uplift along the faults. Exposed by this erosion were two rock bodies originally formed deep below the Earth's surface. Pinto Gneiss, formed 1.7 billion years ago was intruded by molten magma 85 million years ago, which then cooled forming White Tank monzogranite.
There were probably many other geologic events occuring both before and after the formation of the gneiss and intrusion of the monzogranite. However, any record of these events has been lost through erosion. What does remain, what we see today, is the roots of ancient mountains. These roots have been faulted, jointed, weathered and eroded to produced the unique scenery we see today in Joshua Tree National Park.
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| GLOSSARY | > erosion, fault, geologic, gneiss, magma, weathering |
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