The California Highway Patrol said the Lake County man found the bomb shell on his property and decided to drive it Monday to a San Francisco bomb squad for disposal, the Marin (Calif.) Independent Journal reported Tuesday.
However, the man became nervous about two hours into his drive and decided to call authorities around 3 p.m. He was instructed to get off the road, so he pulled into Rancho Olompali State Park to wait for police.
The Highway Patrol, Novato firefighters and park rangers responded to the scene and called in a bomb squad.
The 4-foot-long cannon shell was taken by authorities and found to be inert.