Authorities at the John Latorraca Correctional Facility in Merced conducted a search of the dorms and found drug paraphernalia and a cell phone.
During the search one inmate was struck in the head with a bean bag round. The inmate was transported to a Modesto hospital by ambulance for treatment, Merced County Sheriff spokesman Deputy Tom MacKenzie said.
The search was carried out early Friday morning and was ordered as part of an ongoing investigation into contraband and increased violence inside the jail.
The injured inmate was struck with the bean bag when he attempted to hide under his bunk with a mattress. The bean bag hit him after skipping off the floor, MacKenzie said.
Detectives are following up with interviews to determine if charges will be brought against the inmates found in possession of the contraband items. The facility is on lockdown until further notice.