Story highlights The three victims fell 25 feet

The cause of the fall is being investigated

(CNN) A Texas mother died and her two daughters were injured when they fell from a chairlift at a Colorado ski resort, authorities said.

The three fell about 25 feet from the lift Thursday morning at the Ski Granby Ranch in Granby, Colorado, west of Boulder. They were on vacation at the time of the accident, Schelly Olson, a spokeswoman for the Grand County Sheriff's Office, told CNN. The victims' identities were not immediately available.

The woman, 40, was pronounced dead at Middle Park Medical Center in Granby, Olson said. Her 9-year-old daughter was taken by medical helicopter to Children's Hospital Colorado in Aurora and was listed in stable condition. The 12-year-old daughter was treated at a local hospital and released.

The sheriff's office was investigating Friday, Olson told CNN, talking to lift operators and witnesses to determine the cause of the accident. The Colorado Passenger Tramway Safety Board has also sent an inspector to Granby to investigate, she added.