The quake that struck at about 11:12 p.m. Friday had a preliminary magnitude of 5.4, said Jessica Sigala, a geophysicist with the U.S. Geological Survey in Golden, Colorado.
It was centered 16 miles southeast of the border town of Mexicali and about 100 miles east of Tijuana.
"It has been felt pretty widely in Southern California, southwestern Arizona and probably northern Mexico," Sigala said.
It was followed by at least 25 smaller aftershocks.
The quake left about 400,000 people without electricity and 1.2 million without cellular telephone service, but service was restored at around 4 a.m. local time, said Fire Capt. Rene Rosado, director of civil defense in Mexicali.
About 80,000 workers were evacuated or were unable to enter local factories for Sony, Honeywell and other major corporations that typically run 24 hours a day until the buildings could be checked for damage, he said.
Many residents had returned to work Saturday morning, and a group of 70 rescue workers traveled from Tijuana to Mexicali to assist in assessing the damages, Rosado said.
Two bridges showed 2- to 3-inch cracks and were closed until engineers could determine they were safe, he said.
Rescue workers were examining Mexicali schools, many of which are made of adobe, for cracks and other damage so students could return to classes safely Monday, said Alfredo Escobedo, director of Baja California civil protection.
A magnitude-5.4 temblor struck the Mexicali area in 2006, but there were no injuries or damage.
