The 4.7 magnitude temblor hit at 9:55 a.m. local time, causing buildings to shake from San Diego and Los Angeles eastward to Arizona.
Seismologists say the shaking was felt so widely because the epicenter was in the San Jacinto Mountains, which are composed of hard granite that conducts ground motion more efficiently.
The U.S. Geological Survey said the quake occurred at a depth of about 8 miles along the San Jacinto fault zone, which cuts through San Bernardino, Riverside, Imperial and San Diego counties.
It runs roughly parallel to the more famous San Andreas fault.
There were no reports of significant damage or injuries from the shaking, but some items were tossed off shelves.
The quake was described as a slow, swaying motion that lasted about 10 seconds.
Hundreds of aftershocks struck the same area for days after the initial Monday quake.