Answer:
Movements of the tectonic plates
Step-by-step explanation:
Earthquake activity in California is primarily caused by the movement of the tectonic plates that make up the Earth's crust. California lies along the boundary where the Pacific Plate and the North American Plate meet, which is known as the San Andreas Fault. The movement of these plates causes stress to build up in the Earth's crust, which can lead to earthquakes. Additionally, there are many other faults in California, both large and small, that contribute to earthquake activity in the state.