There has been a little activity in the Yorba Linda, CA area over the past 24 hours, starting with an M4.5 at 11:23pm local. Another M45 occurred just 10 hours later in the same location, which had M3.7 aftershock not 20 minutes after.
I took some time to put together some quake history into Google Maps.
Small light blue dots are background seismicity. (SCSN catalog 1932-present)
Dark blue dots are the July 29, 2008 M5.4 Chino Hills quake and aftershocks.
Red dots are the September 3, 2002 M4.8 Yorba Linda quake and aftershocks.
The green dot is an October 4, 1961 M4.4 quake.
Orange dots are the current quakes.