A 13-year-old Montana girl was killed and a 7-year-old had to be flown to Denver for medical treatment after a crash Saturday afternoon on Interstate 25.

The crash occurred at milepost 294 near Buffalo when a 62-year-old woman fell asleep at the wheel, according to a crash report from the Wyoming Highway Patrol.

Once the driver fell asleep, the Chevrolet Equinox drifted off the right side of the road, went into a ditch and traveled through a right-of-way fence. The Equinox then went down an embankment, hit a road approach, vaulted across a paved driveway and hit the ditch on the other side, causing it to flip end-over-end roughly one and a half times.

The driver, who was properly restrained, was taken to Johnson County Healthcare Center in Buffalo before likely being transferred to Billings, Montana for treatment.

A 13-year-old girl in the front passenger seat, who was wearing her seat belt, was taken to Johnson County Healthcare Center and died of her injuries.

An unrestrained 7-year-old in the back seat was flown to Denver for treatment.

Weather was clear and the road surface was dry at the time of the crash, according to the Patrol's report.

Driver fatigue is listed as a possible contributing factor.