Joni Mitchell -- Legendary '60s Singer Hospitalized

3:00 AM PT -- Joni is still in intensive care, but her people say she is "awake and in good spirits." We've learned she had a surgical procedure some time after arriving at the hospital on Tuesday.

Singer-songwriter Joni Mitchell -- who's synonymous with the Woodstock generation -- was rushed to a hospital after a 911 call from her home Tuesday.

Sources tell us paramedics went to 71-year-old Mitchell's Los Angeles home around 2:30 PM. We're told the 911 call was for an unconscious female, but she was alert on the way to the hospital.

Mitchell was in intensive care late Tuesday. It's unclear what prompted the medical emergency, but it appears to be quite serious.

We've put in several calls to Joni's rep ... but haven't heard back.

Mitchell's best known for her hit, "Big Yellow Taxi" ... which the Counting Crows famously covered in 2002. She was inducted into the Rock and Roll Hall of Fame in 1997.