"The outage appears to be related to a procedure an APS employee was carrying out in the North Gila substation, which is located northeast of Yuma," an APS press release said. "Operating and protection protocols typically would have isolated the resulting outage to the Yuma area. The reason that did not occur in this case will be the focal point of the investigation into the event, which already is underway."
In other words the real cause has not been identified yet, or it has been identified and the spin doctors are working on a means to explain it away.
Also note that ley lines ("power grid") "connect" Yuma and the L.A. area. Perhaps the outage was deliberate, as a means of giving us a taste of the impending dark Green age, and those behind it are using the opportunity to drop a hint about the Earth Grid ("it started in Yuma").