There are hundreds of earthquakes in California every year, but most of them are so small humans can't even feel them.
California's most-famous earthquake shook up San Francisco in 1906 -- a magnitude 7.8 quake that caused 3,000 deaths and $524 million in property damage.
Vibrations produced by earthquakes -- even the small ones people can't feel -- are detected, recorded, and measured by instruments called seismographs. These devices may amplify ground motions beneath the instruments to over 1 million times. The ground motion activates a writing arm on the seismograph, which translates the ground motion into a wiggly trace pattern called a seismogram. Scientists look at the seismogram to learn things about the earthquake -- such as how big it was and how deep in the ground it took place.
And in a non-earthquake related bit of information: The saber-toothed cat is California's Official State Fossil!