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.