It could take months to pinpoint what caused two high-voltage transmission lines to trip near Medicine Bow last week, resulting in an unprecedented blackout that impacted about 100,000 customers of multiple utility companies across Wyoming, Montana and South Dakota.

The investigation will focus on the sequence of events leading up to the Thursday afternoon outage that began around 4:45 p.m., according to David Eskelsen, a spokesperson for Utah-based Rocky Mountain Power, which had the most customers without power.

“The reason this takes time is that we must examine the data recorded by our system monitoring,” Eskelsen, who declined to speculate on the cause of the blackout, said in an email Tuesday. “We want to be thorough before we draw any conclusions.”

The outage temporarily removed

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