Sheriff's deputies, along with Sonoma police officers, firefighters and emergency personnel responded at 1:16 p.m. and found a single engine Qualt aircraft in a grassy area between a series of warehouse buildings along 21877 Schellville Road.
The pilot and a passenger were extricated from the plane and airlifted to separate hospitals with moderate injuries.
It appears that the plane crashed nose first almost immediately after departing from Sonoma Skypark Airport, according to the sheriff's office.
A cyclone fence was broken, but there was no damage to any nearby buildings.
Witnesses described the engine noise as being under low power, according to the sheriff's office.
The Federal Aviation Administration and National Transportation Safety Board are investigating the cause of the crash.