The fault line that runs through California is the San Andreas Fault.

The San Andreas Fault is one of the most well-known fault lines in the world and a major source of seismic activity in California. Stretching approximately 800 miles, this transform fault marks the boundary between the Pacific Plate and the North American Plate. Its movement has been responsible for many significant earthquakes, including the devastating 1906 San Francisco earthquake. The fault runs from the southern region of California up through the San Francisco Bay Area, making it a critical area for earthquake monitoring and preparation. Efforts to understand the fault are essential for earthquake prediction and safety.