The Los Angeles County Fire Department says the private plane went down late Sunday morning in a remote area near Agua Dulce.
The department confirms four fatalities and says the coroner and Federal Aviation Administration officials are responding.
Agua Dulce is in the Sierra Pelona Mountains about 40 miles (73 km) north of downtown Los Angeles.
FAA spokesman Allen Kenitzer says the aircraft was manufactured by Cirrus but he did not immediately have additional details about the crash. He says the FAA and the National Transportation Safety Board will investigate.