San Quentin Rehabilitation Center in San Quentin, California, 2015.ReutersCalifornia officials confirm that a "potential gastrointestinal illness" has struck at San Quentin.Four prisoners told BI that last Wednesday's boiled chicken was to blame.A July 4th weekend lockdown affecting some 2,000 inmates is only now being lifted, they said.Usually, when "chicken hindquarters" is on the dinner menu at San Quentin, it's good news."It's a very popular meal in prison," Aaron Ramzy, who is incarcerated there, told Business Insider in a phone call from his cell unit Wednesday.