From Oregon Public Radio (NPR):

The stakes are huge: about one-fifth of the nation’s mortgage debt is held in California. A recent study by the nonprofit R Street Institute estimates that Fannie and Freddie’s uninsured earthquake exposure at more than $200 billion. The report warns that private banks, too, are exposed which it calls “a failing for the banking industry and a potentially catastrophic taxpayer hit if a major quake catastrophe occurred.”