The single-engine Cessna went down in Joseph Canyon, just at the edge of the Cleveland National Forest near Corona.
Witnesses say the plane appeared to lose power. They heard the pilot revving the engine just before impact.
The plane splintered from the force of the crash and set off a one-acre brushfire.
Investigators say the damage was so extensive, they could not read the plane's identification number.
The names of the victims have not been released.