Railroad officials say at least one broken bolt holding the rail in place caused the fiery derailment of a Union Pacific train moving volatile crude oil through the Columbia River Gorge on the Oregon-Washington border.

Union Pacific spokesman Justin Jacobs said Saturday that the company filed a report Friday with the Federal Railroad Administration citing one or more broken bolts as the cause of the June 3 derailment.

Jacobs says the bolt is used in curved sections of track and the company is not aware of any previous failures.

He says the company is now in the process of checking similar bolts in curved sections of its 32,000 miles of track in 23 states.

No one was injured in the derailment, but the tiny town of Mosier, Oregon, was evacuated.