VACAVILLE, Calif. -- Two minimum-security inmates at the California Medical Facility in Vacaville were still at large and their quarters, known as "The Ranch," remained under lockdown, prison officials said.

Juan F. Lopez, 28, of Sacramento County, and Gonzalo Ortega, 33, of Napa County were reported missing after a bed check at 9:30 p.m. Saturday. The two were last seen around 8 p.m., public information officer Lt. Dionne Hudnall said.

Officials activated an escape pursuit plan that consists of sounding a horn every half-hour for two hours and notifying local police departments, Hudnall said.

The Ranch houses 161 minimum-security inmates and the facility has 3,059 total inmates in two separate facilities, Hudnall said.

Lopez is 5 feet 8 inches, 150 pounds and has black hair and brown eyes with a medium build and medium complexion. He was serving a six-year term for conspiracy of a crime with a firearm and possession of a controlled substance, Hudnall said.

Ortega is 5 feet 5 inches, 130 pounds with brown hair and brown eyes with a medium to large build and medium complexion. He has been at The Ranch since 2005 and is serving a 12-year term for transportation and sales of a controlled substance, Hudnall said.

The Ranch will remain locked down until the investigation of the inmates' escape is completed but normal operations continue at the rest of the California Medical Facility, Hudnall said.