What is San Andreas fault?

A great scar in the earth's crust runs for almost 600 miles (960km) along the coast of California. This is the San Andreas Fault, where the Pacific plate slowly grinds along the North American plate. The crack of the San Andreas Fault marks the boundary between two plates. During an earthquake, the ground on both sides of the fault can move by up to 39 feet in a few seconds.

a fault line that goes all the way through California and has the potential to cause a major earthquake