A string of earthquakes hit northern Baja California, sending shock waves into California.
Minutes later, a second quake -- magnitude 4.9 -- struck in the same area.
Local news from across Southern California
Buildings briefly swayed in San Diego, which is about 100 miles away, The Associated Press reported.
In Mexicali, five hospitals were briefly evacuated, 90,000 customers lost electricity for 14 minutes and cell phones failed to work for 20 minutes, said Rene Rosado, director of the city's civil defense.
There was "minor damage" to several buildings in Mexicali, a city of 750,000 people and capital of Baja California state, said Alfredo Escobedo, the state civil defense director.
In Calexico, a California city of 40,000 people across the border from Mexicali, crews found no damage to bridges, buildings or roads, said City Manager Victor Carrillo.
"Basically it was a quick, shake-and-bake, jolt-type of thing that seemed to last 15, 20 seconds, 30 seconds at the max," said Carrillo, who was in a meeting at City Hall during the quake. "I have quite a few items on the shelves in my office and they're all intact."
Citizen reports to the USGS indicated it was also felt in southern Nevada and metropolitan Los Angeles.