On December 11, 1997, about 0535 hours Pacific standard time, a Saab 340B, N329AE, operated by American Eagle as Flight No. 3331, experienced severe turbulence in-flight at 5,000 feet msl over Ventura, California. There was no aircraft damage reported. There were no injuries to the 2 flight crewmembers or to the 14 passengers; one flight attendant received serious injuries. The flight departed Santa Barbara, California, at 0510 on an IFR flight plan en route to Los Angeles, California. Visual meteorological conditions prevailed. The aircraft performed an uneventful landing at Los Angeles International Airport. Twenty minutes into a smooth flight, and 10 minutes from landing, the captain reported that he felt some light "chop" so he turned on the fasten seat belt sign. Shortly thereafter they experienced sudden and violent severe turbulence. At that time, the flight attendant had completed her service and was about to acknowledge the seat belt sign over the public-address system prior to her being seated for landing. According to the crew there was no valid sigmet issued and no airmet or pireps were available.