Mountain Geology 


California is a state of many landscapes. There are hills, valleys, coastlines, mountains, and deserts. This wide variety of landforms make our state very unique. The San Bernardino Mountains in Southern California are in the middle portion of a range of mountains known as the Transverse Ranges.

The word transverse means “crosswise direction.” They are named this because most mountain ranges go from north to south, but these mountains go from west to east. Starting in the Pacific Ocean west of Santa Barbara, this mountain range goes inland to the Mojave Desert, forming a physical barrier which divides the central and southern regions of California.

View of the San Bernardino Mountains facing west toward the San Gabriel Mountains.

These mountains are very steep and rugged, especially on the south side. Many geologists, or people who study land formations, believe that they are among the world’s youngest mountains - only about 18 million years old. They are also among the fastest growing chains of mountains in the world. This is because they developed as a result of movement along the San Andreas fault.

The San Andreas fault is the boundary line of two great tectonic plates, or land masses - the Pacific Plate and the North American Plate. When these plates grind against each other, sometimes they cause the earth’s crust to uplift, or buckle up, and make ridges. We feel this movement as an earthquake.

The land around the San Andreas fault has uplifted in many areas. Our mountains are one of these places. Each time we have an earthquake along our section of the fault line, our mountains grow a little taller. Over the years, the ground has been pushed and squeezed together. This is why there are many types of rocks in the San Bernardino Mountains. Although the mountains are mostly igneous rocks such as granite, there are also some sedimentary and metamorphic rocks. By studying these rocks, scientists have learned the story of how our mountains came to be.

  Questions to Think About

1. What is an example of a landform?

2. What is the mountain range that Lake Arrowhead is in?

3. What effect has the San Andreas fault had on the San Bernardino Mountains?


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