A routine repair in Yuma, Arizona caused the massive power outage last week.  But why it spread to such a large are remains under investigation. Michael Milstein with the Bonneville Power Administration says they hope to learn from the outage. They had a similar, but worse incident here in 1996 when a tree hit a power line. One factor in the outage that hit the southwestern U.S. is the above normal temperatures. The grid was near its limits and when the failure happened, and causes a cascading effect of outages.