Seven people have been killed in the United State's 33rd mass shooting so far this year.
The attack happened at a mushroom farm at Half Moon Bay, south of San Francisco.
The 67-year-old suspect, named Zhao Chunli, was arrested shortly afterwards when he drove to a police station.
This is California's second mass shooting in three days, and Assembly member Marc Berman says he went straight from a Montery Park vigil to hear about the latest shooting.
San Francisco Chronicle reporter Jill Tucker spoke to Guyon Espiner.
