In many ways, California prison system officials have been among the most reluctant to adopt systemic changes, experts say, doing so only when forced by the federal courts. Even then, lawyers and advocates for prisoners say, the changes have come slowly and unevenly.

Mr. Brown, a Democrat, has aggressively fought several federal court orders in the two years since the United States Supreme Court ruled that conditions and overcrowding in the system amounted to a violation of the Eighth Amendment — cruel and unusual punishment. Since then, federal judges overseeing the case have repeatedly declared that the state was not making changes quickly enough, and that conditions in the prisons remained appalling — that the state had been “deliberately indifferent.”

The judges have twice threatened to hold the governor in contempt if he does not comply with their order to release prisoners. Last week, Mr. Brown appealed to the Supreme Court to stop the order, arguing that the system had already improved drastically and that stopping the release of prisoners was essential for public safety.

Though the current hunger strike is focused on the state’s solitary-confinement policy, which allows inmates with gang associations to be held in isolation cells for decades, advocates and lawyers for the prisoners say that the widespread participation is a clear sign that the inmates are increasingly infuriated by the conditions. Roughly 12,000 inmates went without state-issued meals for four consecutive days, down from 30,000 on the first day but more than double the number who took part in a similar strike two years ago.