Power outages reported in southern California, Arizona, Mexico

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CNN.com:

(CNN) -- Authorities were investigating a power blackout in parts of southern California, Arizona and Mexico on Thursday that left more than 1 million customers without power and caused widespread traffic jams.

San Diego Gas & Electric said all of its 1.4 million customers were without power. The problem appeared to have originated in Arizona, the utility said.

"This caused our line from AZ and from the north of our region to both trip off," the utility posted on its Twitter account.

"Think of the system as linked by springs, when one part goes out the rest are affected," another Twitter post from the utility said.

Power outages in California stretched from San Clemente to the state's border with Mexico on Thursday, a San Diego County spokesman said.