The incident was reported at 8:30 a.m. off Conn Creek Road by someone who heard screaming, according to the CHP.
The truck went 100 yards into a canyon and turned onto its side, trapping the driver, CHP officials said.
Napa County fire fighters had to carry the driver up a 250-foot embankment before he could be air lifted to the hospital.
His injuries are described as moderate to major.
ABC7 News contributed to this report.