Saint Francis Dam Disaster National Memorial Act (Sec. 3) This bill authorizes the Department of Agriculture (USDA) to establish the Saint Francis Dam Disaster National Memorial at the dam site in Los Angeles County, California, to honor the victims of the Saint Francis Dam disaster of March 12, 1928. The Forest Service must manage the memorial. (Sec. 4) Within three years of this bill's enactment, USDA must submit to Congress recommendations regarding: the planning, design, construction, and long-term management of the memorial; the proposed boundaries; a visitor center and educational facilities; and ensuring public access to the memorial. (Sec. 5) The bill establishes the Saint Francis Dam Disaster National Monument on specified National Forest System land administered by USDA in Los Angeles County for the purpose of conserving and enhancing the cultural, archaeological, historical, watershed, educational, and recreational resources and values of the monument. (Sec. 6) Within four years of this bill's enactment, USDA must develop a management plan for the monument. USDA must manage the monument: (1) in a manner that conserves and enhances its cultural and historic resources, and (2) in accordance with the Forest and Rangeland Renewable Resources Planning Act of 1974. The bill limits the use of motorized vehicles but permits grazing within the monument.