The shooting was reported at about 7:40 p.m. at 9015 Prunedale South Road, according to the sheriff's office.
Sheriff's deputies, along with a gang task force and the California Highway Patrol, responded to a report of a shooting, and the CHP provided immediate medical aid to the girl.
Witnesses described two men with covered faces, one of whom had a handgun, who approached the front yard on foot, according to the sheriff's office.
About six shots were fired, and struck a vehicle, motor home, and a neighbor's front door. The victim was inside the motor home at the time of the shooting.
A dark colored pickup truck was seen speeding from the scene shortly after the shooting, according to the sheriff's office.
The girl was taken to an area hospital where she remains in serious condition.
Anyone with information about the shooting is asked to call the investigations bureau of the Monterey County Sheriff's Office at (831) 755-3772 or the anonymous tip line at (888) 833-4847.