Explain earthquakes as the sudden release of stored energy along a fault, and describe California's setting along active fault lines.
Earth's outer layer is broken into huge pieces called plates that grind against each other very slowly. Where two plates meet along a crack called a fault, they can get stuck against each other while stress, a kind of stored energy, builds up over years. An earthquake happens when the built-up stress finally releases all at once, and the ground shakes as that energy travels outward as waves through the earth.
California sits right along the boundary between two major plates, and one especially well-known fault, the San Andreas Fault, runs through much of the state. This is exactly why California experiences earthquakes far more often than most other parts of the country, and why California buildings are often designed with earthquakes specifically in mind.
Mastery looks like: They can explain an earthquake as the sudden release of stored stress energy along a fault and describe why California experiences frequent earthquakes.
Common stumbles: Thinking earthquakes happen completely randomly rather than from stress building along real faults; missing the connection between stored energy and sudden release.