California Code, Family Code - FAM § 3421

(1) This state is the home state of the child on the date of the commencement of the proceeding, or was the home state of the child within six months before the commencement of the proceeding and the child is absent from this state but a parent or person acting as a parent continues to live in this state.

(2) A court of another state does not have jurisdiction under paragraph (1), or a court of the home state of the child has declined to exercise jurisdiction on the grounds that this state is the more appropriate forum under Section 3427 or 3428, and both of the following are true:

(3) All courts having jurisdiction under paragraph (1) or (2) have declined to exercise jurisdiction on the ground that a court of this state is the more appropriate forum to determine the custody of the child under Section 3427 or 3428.

(4) No court of any other state would have jurisdiction under the criteria specified in paragraph (1), (2), or (3).