What happened during a crucial 11 minute time span could reveal the cause last week's massive power outage.
A state-wide task force is investigating the blackout, which left all of San Diego and parts of southern Orange County and northern Baja without electricity for up to 15 hours.
The trouble apparently started at an electrical substation near Yuma, Arizona, when a worker turned off a malfunctioning voltage regulator.
At 3:27 p.m. Thursday, an important transmission line linking the Yuma substation with Phoenix went out of service.
But a spokesman for Arizona's power system says the no one lost power as a result.
It's what happened next that holds the key to the blackout's cause. At 3:38 p.m. Thursday, power went out to 56,000 customers in Yuma.
From there, the blackout rolled through San Diego and Orange Counties and Mexico.
Cal-ISO, which manages the state power grid, will use computer models to recreate how the power outage started and why it spread unchecked.
A Cal-ISO spokeswoman today told NBC 7 San Diego that the investigation will take "quite a while."
And a spokeman for Arizona Public Service, which operates the North Gila Substation, urged every to withhold judgement about what caused the massive outage until the investigation is complete, and not blame anyone, especially the electrician who worked on that voltage regulator at the Yuma substation.