On July 7, 2006, approximately 0800 mountain daylight time, an Airbus A319-131, N839UA, owned and operated by United Air Lines Inc., encountered turbulence at 17,000 feet mean sea level (msl), near Masonville, Colorado. Visual meteorological conditions prevailed at the time of the accident. The scheduled domestic passenger flight was being operated under the provisions of Title 14 CFR Part 121 on an instrument flight rules flight plan. The captain, first officer, 3 cabin attendants and 105 passengers reported no injuries. One passenger sustained serious injuries. The cross-country flight departed Jackson, Wyoming, at 0720 and was en route to Denver International Airport (DEN), Denver, Colorado. According to United Airlines, the airplane was on the RAMMS arrival for DEN descending through 17,000 feet mean sea level. The flight crew and cabin crew all reported that the flight had been smooth, the "fasten seatbelt sign" was off, and passengers were allowed to get up and move around the cabin. According to the passenger, she was exiting the aft lavatory when the airplane encountered some turbulence. She stated that she felt as if she was being "jammed" to the floor, and felt her right ankle and leg "go" before she fell to the floor. There were no airmen's meteorological information (AIRMETS) or significant meteorological information (SIGMETS) issued for turbulence for the area at the time of the accident. No other injuries were reported and the airplane landed without further incident at DEN approximately 0820. Upon arrival in DEN, it was established that the passenger had fractured her right ankle.