The key facts at the top count the earthquakes in or near California that the U.S. Geological Survey listed in the past 24 hours, of any size, and name the largest. The table lists up to 20 of them, largest first, with the place and the time in Eastern time.
What counts as California here
An earthquake is counted when the place USGS names for it is in California, as in "26 km SW of Gustine, CA". So an earthquake offshore or near a state line is included when the place USGS names is in California, and left out when the place USGS names is in another state or country.
When it updates
USGS updates its list of the past day's earthquakes every minute. This page reads that list every few hours and updates at the same address. For larger earthquakes anywhere in the world, see Was there an earthquake today?