California Code, Welfare and Institutions Code - WIC § 4459

The State Department of Developmental Services shall investigate and examine all nonresident persons judicially committed to any state hospital and shall cause such persons, when found to be nonresidents as defined in this chapter, to be promptly and humanely returned under proper supervision to the state in which they have legal residence.  The department may defer such action by reason of a patient's medical condition.

For the purpose of facilitating the prompt and humane return of such persons the State Department of Developmental Services may enter into reciprocal agreements with the proper boards, commissions, or officers of other states or political subdivision thereof for the mutual exchange or return of such person judicially committed to any state hospital in one state whose legal residence is in the other, and it may in such reciprocal agreements vary the period of residence as defined in this chapter to meet the requirements or laws of the other states.

The department may give written permission for the return of any resident of this state confined in a public institution in another state, corresponding to any state home for the developmentally disabled of this state.  When a resident is returned to this state pursuant to this chapter, he may be admitted as a voluntary patient to any institution of the department as designated by the Director of Developmental Services.