Fam. Code, § 3421

(a) Except as otherwise provided in Section 3424, a court of this state has jurisdiction to make an initial child custody determination only if any of the following are true:

(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:

(A) The child and the child’s parents, or the child and at least one parent or a person acting as a parent, have a significant connection with this state other than mere physical presence.

(B) Substantial evidence is available in this state concerning the child’s care, protection, training, and personal relationships.

(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).

(b) Subdivision (a) is the exclusive jurisdictional basis for making a child custody determination by a court of this state.

(c) Physical presence of, or personal jurisdiction over, a party or a child is not necessary or sufficient to make a child custody determination.

(d) The presence of a child in this state for the purpose of obtaining gender-affirming health care or gender-affirming mental health care, as defined by Section 16010.2 of the Welfare and Institutions Code, is sufficient to meet the requirements of paragraph (2) of subdivision (a).