(CNN) -- Guards fired rounds to quell a "major riot" in the main yard of a prison in central California on Friday, a corrections department spokesman said.
It was not clear what triggered the riot at Folsom State Prison. It began around 7:30 p.m. (10:30 p.m. ET), said spokesman Luis Patino of the California Department of Corrections and Rehabilitation.
About 200 inmates were involved in the riot, prison spokesman Lt. Anthony Gentile said in a statement. Seven inmates were injured and were taken to area hospitals with non-life threatening injuries, he said.
Gentile told CNN affiliate KCRA that the disturbance appeared to start on the handball court in the main exercise yard.
There were no fatalities, Patino said. No corrections officers were injured.
Folsom State Prison is about 20 miles from Sacramento. It is the second-oldest state prison, and houses medium-security inmates, according to the department of corrections.
Music legend Johnny Cash performed for inmates and recorded an album there in 1968.