This paper presents a case history study on the geologic investigation and numerical modeling of a reactivated landslide in the County of Santa Clara, California to identify the failure mechanism. The landslide occurred on an approximately 18.3-m high, north-facing slope during March 2011. The landslide measured about 33.5 m in width and about 51.8 m in length. Along the toe of the slope, a residential structure with a swimming pool was built on a cut and fill pad and there are several other structures present along the western side of the pad. The landslide occurred immediately to the south of the residential building and moved northward between the County Road A and the house's side yard. The movement of the landslide resulted in damaging the west-bound traffic lane of County Road A and encroached onto the paved driveway for the residential property. An investigation was performed to identify the failure mechanism of the landslide to conclude whether Road A re-alignment by the County or prominent cutting performed along the lower portion of the slope by the homeowner during 2000 through 2004 contributed to the reactivation of the old landslide deposit. The investigation included site reconnaissance, reviewing available published geologic information, reviewing site-specific geologic and geotechnical data developed by other consultants, and performing numerical modeling. The outcomes of the investigation indicate that the primary causation for the reactivation and failure of the subject pre-existing landslide is the prominent cutting performed along the lower portion of the slope during 2000 through 2004 and water tank cut bench. The Road A re-alignment did not contribute to the reactivation of the old landslide deposit.