San Andreas Fault

Geological fault stretching for 1,125 km/700 mi northwest-southeast through the state of California, USA. It marks a conservative plate margin, where two plates slide past each other (see plate tectonics).

Friction is created as the coastal Pacific plate moves northwest, rubbing against the American continental plate, which is moving slowly southeast. The relative movement is only about 5 cm/2 in a year, which means that Los Angeles will reach San Francisco's latitude in 10 million years. The friction caused by the tectonic movement gives rise to frequent, destructive earthquakes. For example, in 1906 an earthquake originating from the fault almost destroyed San Francisco. Contemporary official figures put the death toll at 700-800, although later estimates put the figure closer to 3,000 deaths caused by the quake and its aftermath.

The San Andreas Fault has mountains on either side, uplifted by the movements of the plates; rivers flow along its course because it represents a line of weakness that can be easily eroded.