Initially, about 6,600 inmates participated in the hunger strike, demanding better food, warmer clothing and improved educational opportunities, the Los Angeles Times reported.
"The conditions are deplorable, the worst a human being can live in," said Victor Amaya, who said his son Alex Amaya, 24, is among the strikers. "These men have done bad things in their lives, but the way they are treating them is completely inhumane."
The strike started at the Security Housing Unit at Pelican Bay near the Oregon border, the California Department of Corrections and Rehabilitation said. It houses some of California's most hard-core offenders, including Alex Amaya. The isolation units are reserved for violent prisoners, many with gang ties.
Terry Thornton, a corrections department spokesperson, said the strike has remained non-violent. Thornton said prison doctors are monitoring inmates and that prison officials are keeping "an open dialogue" with inmates.