SACRAMENTO, Calif.—California prison officials are opening a $24 million treatment center for mentally ill inmates as they urge a federal judge to end his oversight of the state's correctional system.

The 44,000-square-foot building at the California Medical Facility in Vacaville opened Thursday. It includes rooms where inmates will undergo outpatient therapy, as well as offices for therapists.

The state Department of Corrections and Rehabilitation says it has spent more than $1.3 billion since 2009 on facilities to improve inmates' mental health care. That aspect of prison operations is being overseen by a court-appointed monitor.

Corrections Secretary Jeffrey Beard said the treatment center shows that the state is committed to providing a constitutional level of care and that federal oversight should end.