On November 1, 2003, at approximately 1215 mountain standard time, a Boeing 737-500, N956UA, operated by United Airlines as flight 1232, encountered turbulence while on approach to Denver International Airport (DEN), Denver, Colorado. The airline transport captain and airline transport first-officer, 1 flight attendant, and 92 passengers were not injured; however, 1 flight attendant was seriously injured and 1 flight attendant received minor injuries. Instrument meteorological conditions prevailed. The scheduled domestic passenger flight was being conducted under the provisions of Title 14 CFR Part 121. An instrument flight rules flight plan had been filed for the flight from Boise, Idaho, to Denver, Colorado, departed at 1045. At flight level (FL) 310, air traffic control advised the captain that light to moderate turbulence existed between FL170 and FL 200. The flight crew directed the passengers to take their seats and fasten their seatbelts. During the descent, at FL 240, the captain asked the cabin crew to take their seats. At FL 210, the flight encountered "heavy to moderate turbulence with two rapid up-down vertical-G cycles." One flight attendant received minor injuries and another flight attendant received a fractured ankle. The flight continued to Denver without further incident.