Many of the state's largest earthquakes have struck near the junction, where the Pacific, North American and Gorda plates meet. This area also forms the boundary between two infamous threats: the San Andreas Fault system, which runs across most of California, and the Cascadia subduction zone, which goes up to Vancouver Island, Canada.

According to the U.S. Geological Survey, a preliminary 2.1 magnitude quake struck close to Holtville Thursday morning.

The epicenter was situated approximately 5 miles west of Holtville, at a depth of 5 miles.