Authorities say a caregiver at Gold Age Villa, an elderly care home in Loomis, picked the poisonous mushrooms and tossed them into a soup.
Two people died and four others are in the hospital, including the caregiver who made the soup.
Investigators have determined it was an accident - that the caregiver who prepared the meal did not know the mushrooms were poisonous.
The Department of Social Services, the agency that licenses senior care facilities, is investigating.