Terry Thornton, a spokeswoman for the Department of Corrections, said the largest protest is at the state prison in Corcoran, with about 400 inmates refusing food, the Los Angeles Times reported. She said more than 100 had joined the hunger strike at the California Correctional Institute in Tehachapi and 29 at Calipatria State Prison.
The hunger strike began July 1 at Pelican Bay, the supermax prison near the Oregon border.
Corrections Secretary Matthew Cate issued a written statement Thursday saying officials had struck an agreement with the leaders of the strike that included wall calendars, educational opportunities and "cold-weather caps."
The Los Angeles Times said the strikers had demanded an end to a policy that required prisoners seeking to get out of solitary confinement to inform on gang members. It was not clear whether the demand was met.
Officials said this week that 49 inmates had lost about 10 pounds. Prisoner advocates, however, told the Times that many strikers had lost 20-35 pounds and had begun to faint due to starvation.
Prison officials have refused to grant reporters access to the hunger strikers.