The USGS reports a magnitude 5.1 earthquake at 10:47 a.m. local time this morning near the Baja - Sonora border in Mexico. There are reports of mild ground shaking being felt in Yuma.
The quake lies along the southern extension of the San Andreas fault.
update 2-18-11, 21:00: The Yuma Sun describes local residents being 'shaken, not stirred' by the quake, which occurred near where the magnitude 7.2 Easter quake occurred. The USGS is reported saying there was magnitude 3.1 'foreshock' yesterday.