Nelson said an investigation could potentially result in elder abuse charges.
The patients were transported to other homes Saturday for temporary care while new places are found for them.
The facility came to the attention of law enforcement Saturday after paramedics responding to an emergency call found a small staff struggling to care for the residents, Nelson said.
Michael Weston, a spokesman for the California Department of Social Services, told KPIX that social service officials had checked on the facility Saturday and were told the patients would be cared for over the weekend.
"I can tell you that the department has been engaged with this facility for quite a while and there is a history of concerns," Weston said. "Apparently, what happened is that the facility staff felt that they were starting to lose the capability to care for these individuals, so they called for help."