GRANBY, Colo. (AP) — A woman died and her two young daughters were injured after falling from a chairlift at a small Colorado ski area Thursday. 
 
 The 40-year-old Texas mother and the girls, ages 9 and 12, fell 20 feet from a four-person lift onto snow at Ski Granby Ranch, a 400-acre family-oriented resort about 90 miles west of Denver. 
 
 One of the children was hospitalized in stable condition and the other was flown to a children's hospital in suburban Denver for treatment. Investigators have not released any names and have not said what caused the family to fall. 
 
 The woman was from San Antonio, KUSA-TV reported (http://on9news.tv/2hxUOUf ). 
 
 Police spokeswoman Schelly Olson said state regulators who oversee chairlifts are helping with the investigation. 
 
 Deaths from malfunctions or falls are rare in the United States, The Denver Post reported (https://goo.gl/7eSuhj ). According to the National Ski Areas Association, deaths from malfunctions have totaled just 12 from 1973 through October, and there were three deaths from falls between 2004 and October. 
 
 According to an October report by the NSAA, the last death on a chairlift attributed to a malfunction was in 1993. As of the 2015-2016 ski season, the annual fatality rate per 100 million miles traveled on ski lifts was 0.14. 
 
 The latest death comes during one of the busiest weeks of the season for ski resorts in Colorado. 

 GRANBY, Colo. (AP/CBS4) – A mother died and her two young daughters were injured after falling from a chairlift at a small Colorado ski area Thursday. 
 
 The 40-year-old Texas mother and the girls, ages 9 and 12, fell 20 feet from a four-person lift onto snow at Ski Granby Ranch, a 400-acre family-oriented resort about 90 miles west of Denver. 
 
 “Ski patrol arrived, and they, in addition to EMS, transported the patients to Middle Park Medical Center in Granby,” said Schelly Olson with Granby Fire. 
 
 The 12-year-old girl was treated and released from a hospital in Granby and the 9-year-old was flown to Children’s Hospital in Aurora for treatment. Investigators have not released any names and have not said what caused the family to fall. 
 
 Police spokeswoman Schelly Olson said state regulators who oversee chairlifts are helping with the investigation. 
 
 “The lift was operating safely to get everyone else off,” Olson said. 
 
 The Colorado Passenger Tramway Safety Board is now investigating and says the lift will reopen when it’s deemed safe for the public. 
 
 Witnesses to the accident told CBS4 there had been trouble with the lift for the past few days and the lift even stopped for 10 minutes earlier Thursday morning. Each stop of the lift caused chairs to sway and bounce. 
 
 Deaths from malfunctions or falls are rare in the United States, The Denver Post reported. According to the National Ski Areas Association, deaths from malfunctions have totaled just 12 from 1973 through October, and there were three deaths from falls between 2004 and October. 
 
 According to an October report by the NSAA, the last death on a chairlift attributed to a malfunction was in 1993. As of the 2015-2016 ski season, the annual fatality rate per 100 million miles traveled on ski lifts was 0.14. 
 
 The latest death comes during one of the busiest weeks of the season for ski resorts in Colorado. 
 
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 A Texas mother died and her two young daughters were hurt after they fell about 25 feet from a four-person chairlift Thursday morning at Ski Granby Ranch in Grand County. 
 
 Ray Jennings, chief officer for emergency management at Grand County EMS, said first responders were called to the ski area about 10 a.m. The three were taken to the nearby Middle Park Medical Center. 
 
 The 40-year-old woman died at the hospital, and one of the daughters was flown on Flight for Life to Children’s Hospital Colorado. The other child was in stable condition at Middle Park. The girls are 9 and 12 years old. 
 
 It was not clear what prompted the fall, causing the first chairlift fall death in Colorado in 14 years. 
 
 Schelly Olson, spokeswoman for the incident command, said the three were the only ones on the chair when they fell somewhere between the lift’s loading area and summit. The chair remained attached to the line. 
 
 Olson said there were many witnesses: “People on the chairs in front. People on the chairs in back. People on the hill.” 
 
 Chairlift deaths from malfunctions or falls are exceedingly rare in the United States, according to the National Ski Areas Association. Deaths from malfunctions have totaled just 12 from 1973 through October, and there were three deaths from falls between 2004 and October, the NSAA reports. 
 
 Rod Kessler, a ski area spokesman, said they fell from the Quick Draw Express lift. The lift — a detachable quad, which is often called a “high-speed” lift — was shut down “just to make sure everything is in order,” Kessler said. 
 
 This is the lift where 3 people fell at Granby Ranch this morning. One died. pic.twitter.com/g9Drcyeg4H — Lance Hernandez (@lancehernandez7) December 29, 2016 
 
 Jennings said the Grand County Sheriff’s Office and Granby Police Department are investigating, as is the Colorado Passenger Tramway Safety Board. The names of the three have not been released, but officials say they were visiting from Texas with other family members. 
 
 Ski Granby Ranch is about 20 miles west of Winter Park. The small, 400-acre family-oriented resort is known for being a spot for beginner skiers and snowboarders. It has just four chairlifts. 
 
 The last chairlift fall death in Colorado is believed to have occurred in 2002. 
 
 “(Since) that time, there have been 1.7 billion chairlift rides,” said Chris Linsmayer, a spokesman for Colorado Ski Country USA. “It’s super rare. It really doesn’t happen very often, and it’s not something that folks need to concerned about.” 
 
 According to an October report by the NSAA, the last death on a chairlift attributed to a malfunction was in 1993. As of the 2015-16 ski season, the annual fatality rate per 100 million miles traveled on ski lifts was 0.14. 
 
 In 1976, two cars from Vail’s 7-year-old gondola – each carrying six skiers – plummeted 125 feet, killing four people in one of the most deadly lift incidents in the United States. In 1985, a bullwheel at Keystone Resort failed, sending waves down the line that threw 60 people off the Teller Lift, two of whom later died from their injuries. 
 
 In April 2009, a Rhode Island man with no significant medical history died after losing consciousness on a chairlift in Breckenridge. Attempts to revive him at the top of the lift were unsuccessful. 
 
 In January, a skier pushed a snowboarder off an Aspen Highlands chairlift. Thomas Proesel, who was accused of first-degree assault in the case, was found not guilty by reason of insanity. The snowboarder was not seriously hurt.
– Tragedy in ski country: A mother died and her two daughters were injured in a fall from a chair lift at a ski resort in Colorado Thursday. Authorities say the 40-year-old woman from Texas and the girls, ages 9 and 12, fell around 20 feet from the lift onto snow at the Ski Granby Ranch, the AP reports. One girl was hospitalized in stable condition and the other was airlifted to a hospital near Denver, around 90 miles away. The resort's operation director says the three were the only people on a four-person lift and they "came out of their chair" somewhere between the loading area and the summit. Police and state regulators are investigating the incident, which ski industry groups say was an extremely rare event. The National Ski Areas Association says that between 2004 and October of this year, there were just three recorded deaths from ski lift falls. The last chair lift death blamed on a malfunction was in 1993, according to the NSAA. Since the last fatal accident in Colorado, in 2002, "there have been 1.7 billion chair lift rides," a spokesman for Colorado Ski Country USA tells the Denver Post. "It's super rare. It really doesn't happen very often, and it's not something that folks need to be concerned about." Witnesses to Thursday's accident tell CBS Denver that there had been problems with the chair lift over the last few days, with each stop causing the chairs to sway.