The incident was reported around 5:35 a.m. near the Sausalito-Marin City on-ramp, CHP Officer Eric Hohmeister said.
The truck, a 1988 Dodge Dakota, had apparently swerved to the right for an unknown reason and left the highway, crossed over the on-ramp, sideswiped a guardrail and went through a chain-link fence before coming to rest in a drainage canal, Hohmeister said.
The driver was pronounced dead at the scene, although he had suffered no visible injuries, Hohmeister said. The CHP is investigating whether he experienced a medical problem prior to the crash.
There was minor to moderate damage to the truck, and there were no skids marks to indicate the driver applied the brakes, Hohmeister said.