Can your landlord only offer another year lease after already completing a one year lease with him or her? Isn't it CA law that once a one year rental lease is up it automatically rolls over into a month to month should you decide to stay?

I think it's their choice, month to month means you can leave anytime and they could lose money so I'm sure they will push you to sign for a year or move out. Why not just ask them if they would do a month to month or a shorter lease if you want to move soon.