The annual event was an opportunity to practice safety measures and take steps to prepare for the "Big One."
It comes about three weeks after the state Office of Emergency Services warned of a heightened chance of a major earthquake along the southern stretch of the San Andreas fault following a swarm of around 150 small temblors under the Salton Sea. No major earthquake occurred, but that area of the fault is consider overdue for a temblor of a magnitude of 7.0 or above.
"ShakeOut encourages cross-sector, whole community conversation and action about earthquake preparedness, inspiring people to make better decisions for how they can prepare to survive and recover," said Mark Benthien, Global ShakeOut coordinator and outreach director for the Southern California Earthquake Center at the University of Southern California.
Learn More: Tips on how to prepare, protect and recover.
Organizers said 10.5 million Californians were registered to take part in the drill, including nearly 975,000 in the San Diego region -- the majority of them schoolchildren.
According to county emergency officials, the most important thing to do when the shaking starts is to protect your head from items that might fall.
Register Now: ShakeOut.org
They suggest dropping, covering and holding on under a sturdy table or desk. If it's not possible to get under a desk or table, people can get on the ground or floor while covering their head and stay away from hanging fixtures, windows, glass or furniture that could topple over.
The most recent earthquake that was felt around the county occurred June 10. The magnitude-5.2 shaker struck in Anza Borrego Desert State Park, and while it triggered a minor rockslide on Montezuma Valley Road, about 14 miles southeast of Borrego Springs, there was no major damage.
Last year, over 43 million people participated in Great ShakeOut earthquake drills.