Topanga Canyon Boulevard, also known as State Route 27, was shut down in both directions Saturday between Pacific Coast Highway and Grand View Drive.
Caltrans shared a video that shows mud and rocks flowing off the unstable hillside.
Crews are working to clear all the debris, but there's no word yet on how long it will take.
Meanwhile, a portion of the Pacific Coast Highway in Malibu was also closed Monday due to a rockslide.