That quake hit just after 9:30 a.m. in the Muscoy area at a depth of just over three miles. A few minutes later, a smaller 3.1-magnitude temblor shook the Rialto area nearby.
About an hour before that, the Rialto are saw two smaller quakes - magnitude 3.0 and 2.8.
People reported feeling shaking in many areas including Jurupa Valley, Eastvale, Ontario and even as far as Redondo Beach. Most callers described it as a jolt or sudden movement.
"I felt it in Garden Grove, in my apartment on the 7th floor," Gregory Christison said on Facebook. "It was a rolling sensation."
Cindy Hecht Sedbrook said she was on the 11th floor of a building in Irvine when she felt the quake.
No damage or injuries were immediately reported.
How to make your own earthquake kit
This comes just days after a massive magnitude 8.8 earthquake struck off Russia's Pacific coast on Tuesday, sparking tsunami warnings -- and evacuations of coastal areas -- in Hawaii and alerts all down the U.S. West Coast.
This is a developing story