Tyler Blake Kimbrell's sister was ejected and unhurt, but his 11-month-old niece Breleigh went over the cliff with the car.
Kimbrell raced to the car and used the light on his phone camera as he worked to free her.
In the video, Kimbrell can be seen scrabbling to reach Breleigh. "She's alive!," he says to his sister, before instructing her to call 911 immediately.
"Uncle Blake's going to get you out of here, I promise, I promise," said Kimbrell. "If it's the last thing I do, uncle Blake's going to get you out of here."
By the time he got Breleigh out, firefighters arrived to the scene. He says his niece was not seriously hurt.
Watch the entire rescue in the video below.