San Bernardino County fire Capt. Ed Noble says authorities were called to the home in Grand Terrace shortly before 8 a.m. Tuesday.
He says a slide undercut part of the home's patio and went back some 15 feet. Chunks of foundation fell about 150 feet downhill.
Noble says the home has been red-tagged as unsafe and two occupants will be out until engineers can decide what to do.
The cause of the slide is under investigation but Noble says it may have stemmed from a broken water pipe.
There's a shopping center at the bottom of the hill but Noble says it and surrounding homes aren't considered threatened.