Tornado Captured Touching Down in North Dakota

This photo taken on Monday, May 26, 2014 and provided by Jill Helmuth, shows a tornado touching down on a reach before heading towards Watford City, N.D. Authorities say several were injured and more than a dozen trailers were damaged or destroyed Monday evening when the twister tore through a camp where oil field workers stay. (AP Photo/Jill Helmuth) Jill Helmuth / AP

A tornado that critically injured a 15-year-old girl and hurt eight other people at a workers' camp in the heart of North Dakota's booming oil patch was an EF-2, the National Weather Service said Tuesday.

The twister touched down Monday night at a camp just south of Watford City, about 50 miles southeast of Williston, and damaged or destroyed 15 trailers.