Ferrets are listed as predators and were originally imported to the U.S. in the 19th century to kill rodents. The California Department of Fish and Game claims that when they get loose, they threaten native wildlife, they bite and they could become rabid.
Write letters explaining the nature of ferrets and what great house pets they are to your State Representative. Ask friends and neighbors to join you with signing the letters. Check online for groups that are working towards legalizing ferrets as pets in California. Write your own petition and ask as many people as you can to sign them.