Northern California rescuers pulled the woman from a car that was prevented from falling another 244m when it hit a tree on Tuesday (Wednesday NZT) in Napa.
A California Highway Patrol flight officer and paramedic told the Napa Valley Register it was fortunate the cyclist witnessed the plunge because otherwise it was likely no one would have spotted the wreck on the wooded mountainside.
The cyclist called emergency services and climbed down the slope to reach the 20-year-old victim.
A helicopter lowered paramedics through a small gap in the tree cover, removed the car's windshield and hoisted the woman out.
The newspaper reported that Karla Hernandez-Zambrano suffered major unspecified injuries and was in stable condition in a hospital.