The largest number of reports of today's early morning (3:52 am local time) magnitude 5.0 earthquake in Baja California, are coming from San Diego and Yuma, Arizona. As of 1pm, Yuma had about 225 responses to the quake being felt.
The event looks like an aftershock to the April 4, magnitude 7.2 El Mayor - Cucapah quake. [right, location map from USGS]