Introduction: Geology and the Park
The face of the earth at any time represents only a fleeting moment in a very long history. Major changes are going on all around us, and the way the earth looks now is a dynamic product of these changes. Geology is the science that deals with these changes. This science may be defined as the the study of the processes operating within and on the earth at the present and as revealed by evidence in the rock record, throughout most of its past of 4.5 billion years.
Intrusions
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.
Wash
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 |
