The San Jose Mercury News (http://bit.ly/V2cJRo) says the 69-year-old woman had left a shopping center parking lot on Sunday afternoon and took the Almaden Expressway onramp to state Highway 85.
The California Highway Patrol says the ramp quickly turns left but the woman's car continued straight and wound up in a retention pond.
Santa Clara County sheriff's divers pulled the woman from the sunken vehicle and she was pronounced dead at a hospital.
Her name hasn't been released.
Information from: San Jose (Calif.) Mercury News, http://www.mercurynews.com