Stress on the Earth's crust causes it to deform and change shape, creating distinct landforms. A fault is a crack in the Earth's crust where one side drops, leaving the other side higher. Folding takes place when the Earth's crust is compressed together. When it bends and folds upward, it's called an anticline. When it folds downward, it's called a syncline. Anticlines are good sites for finding oil reservoirs, and synclines are good for tapping groundwater aquifers.
Block mountains form when the layers of the Earth's crust are forced upward near fault lines. Fault-block mountains have a steep, sharp front side and a gentler, sloping back. Examples of block mountains are the Teton Range of Wyoming, the Alps in Europe and the Urals. California's Sierra Nevada is a 350-mile long block of granite containing Mt. Whitney, the highest mountain peak in the lower 48 states. This granite mountain was lifted during the formation of the Basin and Range Province, centred in Nevada and stretching from southern Oregon to west Texas.
When a depression appears between two block mountains, that depression is called a rift valley, which can be thousands of miles long. In the United States, one example of these flat-bottomed valleys is Death Valley in California. Some of the largest rift valleys include the East African Rift Valley, Russia's Baikal Valley, Germany's Rhine Valley and the Red Sea. Ocean rift valleys occur where tectonic plates on the seafloor spread apart. The largest lakes in the world are all found in rift valleys.
Folded mountains form when crust and rock formations lift and fold after tectonic plates collide. These mountains are generally less rough-looking and are formed adjacent to the sharper, thrust-faulted block mountains. The Appalachian Mountains in the eastern United States are folded mountains. Other examples include the Rocky Mountains, Himalayas in Asia, the Andes in South America, the Jura Mountains near the Alps, and the Zagros Mountains in northwestern Iran.
A strike-slip fault happens where geologic stresses occur in two tectonic plates parallel to each other. The best known example of a strike-slip fault is the 800-mile long San Andreas fault in California, created by the Pacific plate colliding with the North American plate. The San Andreas and Garlock faults intersect in Southern California. At this point, the movement of the Earth's crust at the Garlock fault bends the San Andreas fault into an "S" shape. This pushing together of the crust has resulted in the formation of the San Gabriel Mountains north of Los Angeles.
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