The ShakeOut is an annual drill aimed at teaching people what to do in the event of an earthquake, while encouraging readiness for the big one.
Participants fell to the floor to practice the "drop, cover and hold" technique -- the recommended procedure in an earthquake.
"The concept of drop, cover, hold on is really simple. You drop down, protect your head, and no one is going to get hurt from that," said Chester Bosworth, a student at Providence High School.
People should quickly get under a sturdy table to avoid being hit by falling objects, or get on the ground next to an interior wall and cover their head and neck with their arms. People should also face away from windows and mirrors, and stay indoors instead of running out in panic.
After an earthquake, people are advised to remain calm; check for damage; learn in advance what to do about fire, leaking gas, electrical dangers and chemical spills; and brace for aftershocks.
A 2008 report estimated there is a 50 percent chance of a magnitude-7.8 or greater earthquake somewhere in California anytime in the next 30 years.
City News Service contributed to this report.