The Legendary San Andreas Fault is at least 10 miles (16 km) deep and runs for some 800 miles (1,280 km) through western and southern California. The fault is caused by the meeting and shifting of the Pacific and the North American Plates and forms the boundary between the two. Earthquakes occur along this boundary.
These plates move past one another very slowly but not continuously. Thus years will pass when they simply push against each other, but when the build-up of pressure breaks open the fault the plates will lurch several metres. The shock waves orchestrated by this activity are what we call earthquakes.
The San Andreas Fault is quite visible as a linear trough, particularly from the air, though on the ground it can be clearly seen on the Carrizo Plain. Here on this long, arid, treeless plain, geological research has been conducted since 1908, two years after the devastating San Francisco earthquake. Studies have shown that large earthquakes have occurred in this region roughly every 150 years past 1,500 years, making it a potential danger area the last large quake in the central section of the fault was in 1857.
Although it is impossible to prevent earthquakes, structures can be built to withstand them. Intelligent design and a good warning system may prevent great destruction when, inevitably, the next large earthquake occurs.
Here on Carrizo Plain, streams can be seen turning sharply north as they cross the fault line, and small, undrained, salt-laden ponds containing brine shrimp also feature. In the centre of the plain lies Soda Lake, which forms each winter and provides a habitat for migratory birds. Having no outlet, the lake evaporated during summer, and the salts that are left are blown skyward in great white columns.