San Diego experienced widespread outages Thursday, with up to 5 million people affected. By early Friday morning, power had been restored to 710,000 customers in San Diego County, and lights were back on late Thursday for consumers in Arizona and California's Orange and Imperial counties. Millions, though, were still in the dark. San Diego Gas & Electric said Thursday night that power could be out "into the night," with some estimating it wouldn't be restored until Saturday. The cause of the blackout is still being investigated, but officials said unusually high temperatures could be a cause and it was not the result of terrorist activity. All inbound flights were halted due to the outage, two nuclear reactors at the San Onofre power plant were shut down and all San Diego area schools were closed Friday.