The Robinson R66 helicopter crashed at around 1:15 p.m., local time, on Sunday (20:15 GMT) in a remote area of the county north of Sacramento, according to the US Federal Aviation Administration (FAA).
The Colusa County Sheriff's Department confirmed to The San Francisco Chronicle that all four people on board died in the crash.
The cause of the crash is under investigation, according to the US National Transportation Safety Board (NTSB).
"NTSB is investigating the August 1, 2021, crash of a Robinson R66 near Colusa, California," NTSB said on Twitter.
CBS reported citing authorities that the crash occurred near Highway 45 at Reservation Road near Colusa.