sentences:  A mistake by an Arizona Public Service employee at the North Gila substation resulted in the loss of a 500 kV line supplying San Diego Gas & Electric's North Gila-Imperial Valley segment on the Southwest Power Link  causing one of the largest power outages in history for the Southern California region.Had the utilities affected realized the consequences to the loss of this line, they would have taken steps to eliminate the vulnerability.On April 27, 2012, the Federal Energy Regulatory Commission and the North American Electric Reliability Corporation released their report detailing the blackout and its causes.