California (San Francisco Area) was also heavily immigrated by mainly Northern Italians, more so than in the Eastern cities of the US which were mainly Southern Italian immigrants. LCN isn't as prevalent within the Northern Italian culture as it is ingrained into Southern Italian and Sicilian cultures. Northern Italians also tend to have lighter features and I am guessing maybe had an easier time obtaining jobs in the US after they immigrated to California and didn't endure as much prejudices and racism as their Southern Italian counterparts endured back in the Eastern United States, just a speculation on my part?

http://bancroft.berkeley.edu/collections/italianamericans/