Authorities have not yet determined what specifically precipitated the fight, but it came after a long-running dispute between white and Hispanic prisoners in the 900-inmate minimum-security unit, according to prison officials. Inmates from other buildings also became involved in the fracas before it was over.
The riot lasted about six minutes before about 50 officers were able to stop it using batons and CS.
After the incident, the entire prison was put on lockdown. Officers separated the groups of inmates and put them in plastic handcuffs to safely search for weapons. Five weapons were discovered in the unit, including socks filled with bars of soap, a razor, and a make-shift weapon fashioned from a pen and a metal tip.
Of the 42 inmates injured, three were taken to area hospitals to treat serious injuries.
The last large riot at San Quentin occurred in 1982 and involved 1,000 men.