During 2012, I spent the first 4 months living in California while in a startup accelerator program. I had a California apartment lease with my name on it during that time. I earned income during this time.
It was not my permanent residence; I still maintained and paid rent on my permanent residence in Michigan.
Do I need to file tax documents with the state of California for this period? What are the rules for answering that question?
Actually you're part-resident, not non-resident. Its the same form in California (540NR), but the difference is significant. California taxes its residents on worldwide income. So for the time you were a California resident - all of your income is taxed by California. For all the rest of the time - only the income derived from California.
You can get more details on this FTB site.
Yes, since you have California income. You file as a California nonresident.
