Workers were feeding the horses on the 20-acre ranch around 6:30 a.m. when they heard trees and rocks sliding down a hill.
No people or horses were hurt. One residence was evacuated as a precaution, and 63 horses were relocated.
As of Friday afternoon, the hillside was still moving very slowly. Safety lookouts were posted with horns in case it becomes more serious.
No word yet on what caused the slide.