Earthquake insurance - I'd get it assuming that you're in high risk area. I didn't need it in Sacramento, but would assume you do. However, I don't know the fault lines in SoCal at all.
Natural gas line - so, they're covering damage from the earthquake? Or just in general? If the first, I'd check if the earthquake policy already includes it.
Read the policy docs, and get answers. Also, do you have assets to self insure, at least partially?