I am on H1B since October 1, 2017. I am filing Form 1040 for my Federal taxes, which I will file after May 2018, filing for an extension. How should I file my State tax? I live in California. Does California have any provision for treating "part-year residents" as "residents", if filed for an extension?
If you moved into or out of California in the middle of the year, then you are a part-year resident of California -- resident only for the part of the year you resided in California. This has nothing to do with whether you are a "resident alien" or "nonresident alien" for federal tax purposes.