CORCORAN, Calif. -- A correctional officer was stabbed by an inmate Tuesday at the state prison at Corcoran.

The female guard was stabbed in the head with a makeshift weapon in a housing unit at the Substance Abuse Treatment Facility, according to prison public information officer Michele Kane.

The unidentified officer was treated at a hospital and released. There were no other injuries, Kane said.

Prison officials hadn't determined a reason for the attack as of Tuesday night. The prison was placed on lockdown while the investigation got underway.