Food safety officials are looking through Setton Farms' plant in rural Tulare County to see if it could lead them to the source of the contamination.
The recalls began last Friday when the Georgia Nut Company recalled its Kraft Back to Nature Nantucket Blend trail mix after some samples tested positive for salmonella. Setton Farms has started a separate recall of roasted pistachios, and grocery operator Kroger also has recalled some pistachio products.
No illnesses have been reported.
The California Department of Public Health said Monday it was tracking nuts processed at Setton Farms, a firm whose Web site describes it as the second-largest pistachio processor in the United States.
State authorities said Setton sent its roasted pistachios to Georgia Nut. Setton Farms has initiated a separate recall of three lots of roasted pistachios tied to the positive results in the trail mix, California officials said.
Kroger said the California firm also supplied the line of pistachios it recalled because of possible salmonella contamination. Those nuts were sold in 31 states.
Setton Farms did not immediately respond to calls for comment.
Dr. David Acheson, director of food safety for the Food and Drug Administration said the contaminated pistachios are not related to a recent outbreak of salmonella tied to peanuts, reports CBS News Correspondent Nancy Cordes.
The one million pound recall figure could grow as the company tracks its products, Cordes reports, and it will likely extend to all manner of pistachio products.
Right now, the FDA is advising Americans not to eat pistachios but not to throw away their pistachios either. Basically, people should hold on to their pistachios until the FDA knows more about which products are affected.