The people who died were adults. The other victims suffered major injuries, including two children, the CHP said.
Authorities used a helicopter in the rural area northwest of Cazadero to reach the wounded people. Firefighters rode ATVs to reach the victims, the CHP said.
The Jeep had been traveling along a dirt road, but it's unknown what caused the crash.
"The scene is chaotic and the investigation has just begun," the CHP said.